UC-NRLF 


°F  TFfE        ^   \ 

UNIVERSITY1 

I  OF 


BEARINGS  AND 
BEARING  METALS 


BEARINGS  AND 
BEARING  METALS 


A  TREATISE  DEALING  WITH  VARIOUS  TYPES 
OF  PLAIN  BEARINGS,  THE  COMPOSITIONS  AND 
PROPERTIES  OF  BEARING  METALS,  METHODS 
OF  INSURING  PROPER  LUBRICATION,  AND 
IMPORTANT  FACTORS  GOVERNING  THE  DE- 
SIGN OF  PLAIN  BEARINGS 


FIRST  EDITION 

FIRST    PRINTING 


NEW  YORK 

THE  INDUSTRIAL  PRESS 

London:   THE  MACHINERY  PUBLISHING  CO.,    Ltd. 
1921 


MACHINERY 


I 


MACHINERY  5$  noted 

for   enterprise  and 

'.thoroughness. 


MACHINERY 

is  all  for 

quality. 


Copyright,  1921,  The  Industrial  Press,  Publishers  of  MACHINERY, 
140-148  Lafayette  Street,  New  York  City 


PREFACE 


FEW  subjects  related  to  the  design  or  construction  of  ma- 
chinery are  of  greater  importance  than  the  subject  of  bear- 
ings. All  classes  of  mechanisms  have  bearings  of  some 
kind  and  bearings  that  are  properly  designed  and  con- 
structed are  a  necessity.  As  every  experienced  mechanic 
knows,  a  poor  bearing  may  tie  up  a  machine  or  even  cause 
an  entire  plant  to  shut  down  temporarily.  Owing  to  the 
importance  of  this  subject,  designers  and  mechanics  in 
general  should  understand  the  fundamental  principles  gov- 
erning bearing  design  and  should  know  what  approved 
types  are  in  common  use  on  different  classes  of  machinery. 

This  treatise  deals  exclusively  with  plain  bearings,  ball 
and  roller  bearings  being  covered  in  another  book  of  this 
series.  The  types  of  plain  bearings  illustrated  ins  connec- 
tion with  the  following  chapters  were  selected  to  show  how 
designs  are  modified  to  suit  different  conditions,  and  also 
practical  methods  of  arranging  bearings  to  insure  adequate 
lubrication  and  thorough  protection  against  the  entrance 
of  any  foreign  material  liable  to  injure  the  bearing  sur- 
faces. The  designs  illustrated  were  taken  from  actual  prac- 
tice and  have  proved  satisfactory  when  properly  con- 
structed and  applied.  This  treatise  contains,  in  addition 
to  the  features  mentioned,  condensed  information  on  com- 
positions of  various  bearing  metals,  their  properties,  the 
classes  of  service  to  which  different  bearing  alloys  are 
adapted,  and  the  general  methods  of  procedure  in  design- 
ing plain  bearings  to  meet  different  service  conditions. 


793278 


CONTENTS 

Types  of  Plain  Bearings 1 

Bearing  Metals   29 

Methods  of  Lubricating  Bearings 59 

Design  of  Plain  Bearings .93 


BEARINGS  AND  BEARING  METALS 


CHAPTER  I 
TYPES  OF   PLAIN    BEARINGS 

BEARINGS  may  be  divided  into  two  general  classes: 
journal  bearings  and  thrust  bearings.  In  the  journal  bear- 
ing the  load  acts  at  right  angles  to  the  axis ;  such  bearings 
are  also  termed  radial  bearings.  In  the  thrust  bearing,  the 
load  acts  parallel  to  the  axis.  Bearings  may  also  be  divided 
into  two  classes  according  to  the  manner  in  which  the  bear- 
ing surfaces  are  in  contact  with  each  other.  Ordinary  bear- 
ings have  a  sliding  contact,  whereas  ball  and  roller  bearings 
have  a  rolling  contact.  In  this  treatise,  bearings  with  slid- 
ing contact  only  will  be  dealt  with. 

Solid  and  Adjustable  Bearings.  In  the  simplest  form  of 
bearing,  a  cylindrical  shaft  fits  into  a  hole  in  the  part  which 
forms  the  support  for  the  shaft.  In  a  bearing  of  this  type, 
there  is  no  provision  for  the  taking  up  of  the  wear  between 
the  shaft  and  the  bearing.  For  this  reason,  a  bushing  or  lin- 
ing is  generally  used  in  the  supporting  machine  part  into 
which  the  shaft  fits.  When  this  bushing  becomes  worn,  it  can 
easily  be  replaced.  Frequently  bushings  of  this  type  are 
made  tapered  on  the  outside  and  fit  into  a  tapered  hole  in 
the  supporting  frame.  The  bushings  are  split  and,  as  the 
hole  in  the  bushing  wears,  means  are  provided  for  pulling 
the  bushing  into  the  tapered  hole  so  as  to  reduce  the  diam- 
eter of  the  hole.  In  other  cases,  the  bushings  are  cylindrical, 
but  the  whole  bearing  is  split,  so  that,  when  wear  occurs, 
one-half  of  the  bearing  can  be  tightened  down  to  restore 
proper  conditions. 

Self-aligning  Bearings.  When  torque  is  applied  to  a  shaft 
and  the  journal  begins  to  move,  the  bearing  should  be  so 


'  2  .; '  ',  PLAIN  BEARINGS 

supported '.that ;it  will  adjust  itself  to  the  journal  and  equal- 
ize the  load  over  the  entire  bearing,  thus  giving  an  oil  film 
of  uniform  thickness  in  a  line  parallel  with  the  shaft. 
Small  bearings  may  not  require  .this  self -aligning  feature, 
the  limits  used  being  accurate  enough  to  give  uniform 
alignment ;  but  larger  bearings,  built  from  a  number  of  as- 
sembled parts,  should  embody  this  self-aligning  principle. 
Years  ago,  engine  builders  adopted  a  ball-and-socket  seat  for 
this  purpose.  Some  manufacturers  prefer  that  design  now, 
and,  for  certain  classes  of  apparatus,  there  may  be  need  for 
some  such  arrangement;  but  for  the  small  limits  of  deflec- 
tion and  the  higher  speeds  now  used  in  machinery  bearings 
generally,  a  simpler  arrangement  is  used.  An  annular  ring 
is  turned  in  the  center  of  the  bearing  shell  for  about  one- 
fifth  of  its  length,  and  this  rests  upon  a  corresponding  sup- 
port in  the  housing;  the  bearing  ring  extends  down  over 
the  sides  of  the  support  to  take  up  the  thrust  due  to  end 
play.  This  is  a  very  effective  and  simple  arrangement  and 
is  the  type  of  support  referred  to  when  self-aligning  bear- 
ings are  specified  in  electrical  machinery,  for  example.  The 
other  type  is  used  for  some  designs,  when  larger  limits  of 
self -alignment  are  necessary,  and  is  known  as  a  "spherical- 
seat  self -aligning  bearing."  This  type  is  especially  used  for 
line  shafting ;  it  has  a  self -aligning  ball-seat  on  the  bearing, 
which  fits  into  a  ball-seat  of  the  bearing  box. 

Characteristics  of  Plain  Bearings.  Plain  bearings  have 
been  developed  to  meet  the  requirements  of  many  different 
conditions  of  service  under  which  shafts  and  spindles  are  re- 
quired to  operate.)  In  all  plain  bearings  there  is  surface  con- 
tact between  the  shaft  and  the  bearing,  and  in  order  to  pro- 
vide for  the  efficient  transmission  of  power  without  exces- 
sive f  rictional  resistance,  wear,  and  tendency  of  the  bearing 
to  give  trouble  through  heating,  a  constant  supply  of  clean 
lubricating  oil  must  be  delivered  to  the  bearing,  and  this 
lubricant  must  be  suitable  for  the  conditions  of  bearing 
pressure,  speed  of  rotation,  etc.  The  effect  of  a  lubricant 
is  to  prevent  direct  metal-to-metal  contact.  Some  authori- 
ties explain  this  action  by  comparing  the  lubricant  to  the 
balls  in  a  ball  bearing.  Where  this  comparison  is  made,  it 


PLAIN   BEARINGS  3 

is  justified  on  the  basis  that  the  lubricant  consists  of  a  mul- 
titude of  small  globules  of  oil  which  roll  between  the  shaft 
and  its  bearing,  thus  preventing  metal-to-metal  contact 
and  greatly  reducing  f  rictional  resistance. 

Plain  bearings  are  made  in  a  great  variety  of  designs, 
according  to  the  conditions  of  service  under  which  they  op- 
erate, and  as  many  of  the  best  designs  are  found  on  machine 
tools,  bearings  for  this  class  of  service  will  be  featured  in 
this  book.  As  a  rule,  when  bearings  are  used  to  support  the 
spindles  of  machine  tools,  where  the  presence  of  any  consid- 
erable amount  of  lost  motion  would  result  in  inaccuracy  of 
work  produced  by  the  machines,  means  of  adjustment  are 
provided  to  take  up  any  lost  motion  that  develops  as  a  result 
of  wear  in  the  bearing.  In  the  detailed  descriptions  of  dif- 
ferent types  of  plain  bearings,  the  manner  in  which  design- 
ers have  worked  out  means  of  compensating  for  wear  will 
be  explained. 

Adjustable  Bearings  for  Machine  Tool  Spindles.  In  de- 
signing the  bearings  for  carrying  the  spindles  of  machine 
tools,  it  is  very  important  to  provide  means  of  constantly 
maintaining  a  tight  fit  between  the  spindle  and  its  bearing 
boxes,  in  order  effectually  to  eliminate  chatter  and  vibra- 
tion. It  is  evident  that  any  lost  motion  in  the  bearings  will 
seriously  affect  the  accuracy  of  work  produced  on  the  ma- 
chine and  the  perfection  of  finish  which  it  is  possible  to  ob- 
tain on  the  work.  Not  only  must  the  bearings  be  a  perfect 
fit  at  the  time  the  machine  is  new,  but  provision  must  also 
be  made  to  compensate  readily  for  any  wear  which  develops 
after  the  machine  is  placed  in  service,  so  that  it  will  con- 
tinue to  produce  work  of  the  required  degree  of  accuracy. 
To  meet  the  requirements  of  this  service,  some  form  of 
tapered  bronze  bearing  has  been  quite  generally  adopted  as 
a  standard  spindle  bearing  construction,  although  various 
modifications  of  this  general  form  of  design  have  been 
worked  out  by  different  machine  tool  builders  to  provide  for 
making  the  necessary  adjustment  for  wear.  These  modifi- 
cations may  be  made  to  meet  the  requirements  of  different 
conditions  of  service  for  spindles  which  are  mounted  in  a 
vertical  or  a  horizontal  position,  or  they  may  be  worked  out 


4 


PLAIN  BEARINGS 


simply  to  meet  the  individual  opinions  of  different  design- 
ers. In  the  following  discussion,  there  are  presented  de- 
scriptions and  illustrations  of  different  well-known  forms  of 
adjustable  spindle  bearing  designs,  which  have  been  found 
to  give  satisfactory  service. 

Grinding  Wheel  Spindle  Bearings.  In  order  to  give  satis- 
factory service,  the  spindle  of  a  grinding  machine  must  ro- 
tate without  an  appreciable  amount  of  vibration ;  otherwise 


E      F      H 


Machinery 


Fig.    1.      Design    of    Spindle    Bearings    for    External    Grinding 

Machine,   showing    Provision    made  to   compensate 

for   Wear   and    Method    of    Lubrication 

chatter  marks  will  appear  on  the  work.  It  is  safe  to  say, 
perhaps,  that  in  working  out  the  design  of  the  average 
grinding  machine,  more  time  is  given  by  the  designer  in  de- 
veloping a  satisfactory  form  of  spindle  bearing  construction 
and  in  modifying  this  design  to  overcome  trouble  which  is 
experienced  when  the  first  machine  is  placed  in  service,  than 
in  producing  satisfactory  results  in  any  other  part  of  the 
mechanism.  In  Fig.  1  there  is  shown  the  standard  type  of 
grinding  wheel  spindle  bearing  which  has  been  adopted 
for  use  on  external  grinding  machinces  built  by  the 
Landis  Tool  Co.,  of  Waynesboro,  Pa.  The  bronze  bush- 
ings A  are  assembled  in  the  housings  in  such  a  way 


PLAIN   BEARINGS  5 

that  expansion  and  contraction,  due  to  changes  in  tem- 
perature, do  not  in  any  way  affect  the  transmission  ef- 
ficiency of  the  bearings;  and  compensation  for  wear 
provided  by  the  tapered  form  of  the  bushings  enables 
all  lost  *  motion  to  be  taken  up,  thus  effectually  elimi- 
nating vibration  and  enabling  the  grinding  machine  to  pro- 
duce perfectly  accurate  work.  Attention  is  called  to  the 
fact  that  adjustment  for  wear  in  the  front  and  rear  spindle 
bearings  is  made  independently,  so  that  if  only  one  bear- 
ing requires  adjustment,  this  can  be  done  without  touching 
the  other  bearing.  On  these  bearings,  lubrication  is  pro- 
vided by  individual  sight-feed  oil-cups,  from  which  a  sup- 
ply of  oil  is  delivered  to  a  reservoir  E  beneath  each  of  the 
bearings.  Felt  wicks  take  oil  from  these  reservoirs  and 
carry  it  up  to  the  bearings,  the  wicks  F  being  held  in  con- 
tact with  the  bearings  by  means  of  compression  springs.  It 
will  be  seen  that  each  reservoir  is  provided  with  a  threaded 
plug  H,  which  may  be  removed  to  drain  out  dirty  oil  and 
flush  the  bearing  with  kerosene  before  the  plugs  are  re- 
placed and  a  fresh  supply  of  lubricating  oil  is  delivered  to 
the  reservoir.  Drains  G  prevent  the  possibility  of  reser- 
voirs E  overflowing  and  flooding  the  bearings.  Oil-distrib- 
uting grooves  /  are  cut  in  the  journals  to  facilitate  the  uni- 
form distribution  of  oil.  The  way  in  which  these  spindle 
bearings  are  adjusted,  will  be  apparent  from  the  illustration. 
Bronze  bushings  A  are  a  press  fit  in  the  housings,  and 
journal  sleeve  B  is  fitted  over  the  back  end  of  the  spindle. 
The  thrust  load  is  carried  by  steel  thrust  washers  C.  When 
it  is  necessary  to  compensate  for  wear  in  the  journal  bear- 
ings, this  is  done  by  releasing  collar  J  and  tightening  L  to 
draw  the  front  bearing  into  its  box  to  take  up  lost  motion ; 
similarly,  lost  motion  in  the  rear  bearing  is  taken  up  by 
releasing  collar  K  and  tightening  L,  which  forces  sleeve  B 
into  the  tapered  bronze  box.  Each  division  on  collars  J,  K, 
and  L  gives  0.00052  inch  of  adjustment  on  the  diameter  of 
the  bearings. 

Self-aligning  Spindle  Bearings.  Features  of  particular  in- 
terest in  connection  with  the  design  of  btearings  for  the 
wheel-spindle  of  a  Brown  &  Sharpe  grinding  machine, 


6 


PLAIN  BEARINGS 


shown  in  Fig.  2,  are  the  provisions  made  for  lubrication 
and  for  the  automatic  alignment  of  the  bearings  with  each 
other.  It  will  be  seen  that  a  sight-feed  oil-cup  is  provided 
at  the  top  of  each  bearing  housing,  from  which  lubricant  is 
delivered  to  the  annular  channel  A  cut  in  the  inside  of 
sleeves  D.  Oil  runs  around  this  channel  and  is  absorbed  by 
a  felt  packing  or  wick  B,  which  is  contained  in  a  slot  cut 
through  the  bronze  bearing  box  on  the  under  side  of  the 
shaft.  This  felt  packing  is  kept  constantly  saturated  with 


Fig.  2.     Another   Example   of    Bearing    Construction   for   Grinding 
Machine    Spindle 

oil,  and  is  held  against  the  shaft  by  a  flat  spring.  As  the 
shaft  revolves  in  the  bearing  box,  the  felt  distributes  a  uni- 
form film  of  oil  over  the  shaft,  thus  efficiently  lubricating 
the  bearing. 

To  assure  accurate  alignment  between  the  two  bearings, 
each  of  the  bronze  boxes  C  is  carried  in  a  sleeve  D  that  is 
machined  to  a  spherical  form  on  the  outside  in  order  to  fit 
into  a  corresponding  spherical  seat  in  the  bearing  housing. 
When  a  straight  shaft  is  put  through  bronze  bearing  boxes 
C,  it  will  be  apparent  that  the  bearings  will  align  themselves 
accurately  on  account  of  the  ability  of  the  spherical-seated 


PLAIN   BEARINGS 


sleeves  D  to  move  as  required  in  the  bearing  housings.  The 
bronze  bushings  C  in  these  bearings  are  tapered  on  the  out- 
side and  bored  straight  on  the  inside;  this  is  not  quite  so 


Machinery 


Fig.    3.       Bearing    for    Table    of     Rotary    Surface     Grinding 
Machine,     showing     Method     of     automatically     com- 
pensating  for  Wear 

usual  an  arrangement  as  that  of  bronze  boxes  which  are 
bored  to  fit  a  tapered  journal  on  the  shaft  they  are  designed 
to  carry.  These  boxes  C  are  split,  and  in  order  to  compen- 


8 


PLAIN  BEARINGS 


sate  for  wear,  it  is  necessary  to  push  the  tapered  outside 
surface  of  the  box  into  the  tapered  seat  in  sleeve  D.  The 
boxes  and  adjusting  nuts  have  beveled  ends  to  keep  the 
bearings  expanded  in  sleeves  D.  First  nut  E  is  loosened, 
and  then  nut  F  is  tightened  sufficiently  to  force  the  bronze 
box  into  sleeve  D  and  cause  it  to  contract  in  a  way  made 
possible  by  the  split  construction.  After  the  desired  adjust- 
ment has  been  obtained  by  tightening  nut  F,  nut  E  is  again 
tightened  against  the  opposite  end  of  the  bearing  box,  thus 
locking  the  box  securely  against  further  end  movement. 


Machinery 


Fig.    4.       Straight    Cylindrical    Spindle    Bearings    provided    with 
Means  of   compensating   for   Wear 

Self-adjusting  Vertical  Bearing.  The  upper  bearing  for 
the  table  or  chuck  of  rotary  surface  grinders  built  by  the 
Persons- Arter  Machine  Co.,  of  Worcester,  Mass.,  is  provided 
with  means  of  automatically  taking  up  any  wear  in  the 
bearing  as  fast  as  it  develops.  The  way  in  which  this  is 
accomplished  will  be  readily  understood  by  reference  to  Fig. 
3,  where  it  will  be  seen  that  steel  collar  A  is  shrunk  on  the 
upper  end  of  the  spindle  and  that  this  collar  is  tapered  on 
the  outside  to  fit  a  bronze  bearing  box  of  corresponding 
form.  This  steel  collar  A  acts  as  a  wedge  in  order  to  keep 
the  bearing  accurately  centered,  although  the  angle  is  such 


PLAIN  BEARINGS  9 

that  the  bearing  runs  quite  freely  and  with  very  little  fric- 
tion. There  is  said  to  be  absolutely  no  chance  for  side  play 
in  this  spindle  bearing  which  would  cause  the  work-table  or 
magnetic  chuck  to  get  out  of  alignment  in  any  direction. 
Collar  A  and  the  bronze  box  in  which  it  runs  are  arranged 
to  form  an  oil  reservoir  from  which  a  constant  supply  of 
lubricant  is  delivered  to  the  bearing,  lubrication  being  facili- 
tated by  spiral  grooves  in  the  taper  collar  which  carry  the 
lubricant  and  distribute  it  uniformly  over  the  rubbing  sur- 
faces. 

Adjustable  Bearing  Box  of  Straight  Cylindrical  Form. 
Still  another  form  of  adjustable  spindle  bearing  box  is 
shown  in  Fig.  4.  This  is  another  Brown  &  Sharpe  construc- 
tion, which  has  been  designed  for  use  in  headstock  spindle 
bearings.  It  will  be  seen  that  this  box  differs  from  any  of 
the  designs  which  will  be  shown  in  this  chapter  in  that  it  is 
of  straight  cylindrical  form  on  both  the  inside  and  outside. 
The  method  of  making  adjustment  of  the  fit  of  this  box  on 
the  spindle  will  be  best  understood  by  referring  to  the  de- 
tailed view  of  the  box  shown  at  A,  where  it  will  be  seen  that 
a  split  extends  all  of  the  way  along  one  side.  Two  dovetail 
slots  B  are  machined  in  this  split  section  to  accommodate 
screws  and  beveled  nuts  or  sleeves  which  may  be  tight- 
ened or  loosened  in  order  to  expand  the  opening  in  the  box 
or  cause  it  to  be  contracted  through  pressure  applied  by  the 
cap  of  the  bearing  housing.  Reference  to  the  end  view  will 
show  that  there  are  two  screws  C  which  hold  the  cap  of  the 
bearing  housing  dov/n  on  top  of  the  bronze  box,  and  when 
it  is  desired  to  secure  a  tighter  fit  of  the  box  on  the  spindle, 
this  result  is  accomplished  by  first  backing  away  the  screws 
in  the  sleeves  in  slots  B  and  then  tightening  up  the  screws 
C  on  the  cap  of  the  bearing  housing.  In  this  way  exactly 
the  required  fit  for  the  bearing  box  may  be  obtained,  and 
after  the  bearing  has  been  in  service,  compensation  for 
wear  may  be  accomplished  by  further  adjustment  of  screws 
C  and  the  screws  which  adjust  the  sleeves  fitting  into 
slots  B. 

Examples  of  Milling  Machine  Spindle  Bearing  Design. 
For  supporting  the  spindle  of  the  vertical  milling  machine 


10 


PLAIN   BEARINGS 


built  by  the  Garvin  Machine  Co.,  Spring  and  Varick  Sts., 
New  York  City,  the  following  construction  has  been  adopt- 
ed :  At  the  lower  end  of  the  spindle,  Fig.  5,  there  is  a  bear- 
ing box  A  which  is  bored  to  a  taper  corresponding  to  the 
tapered  journal  on  the  spindle,  to  provide  means  of  taking 


MacJilnerr 


Fig.    5.     Design    of   Adjustable    Bearings   for    Vertical    Milling 
Machine,   showing    Means   of   Compensating   for   Wear 

up  any  wear  that  may  develop.  It  will  be  seen  that  the 
spindle  is  threaded  along  the  straight  portion  immediately 
above  the  tapered  journal  to  receive  a  threaded  collar  B 
which  provides  for  holding  the  spindle  up.  When  lost  mo- 
tion develops  it  is  easily  taken  up  by  simply  pulling  the 
spindle  up  into  the  tapered  bearing  by  tightening  collar  B. 
To  provide  for  making  this  adjustment,  it  is  necessary  to 


PLAIN   BEARINGS 


11 


face  off  the  soft  washer  between  bearing  box  A  and  the 
spindle  flange.  At  the  upper  end,  the  spindle  is  straight 
and  is  carried  in  a  bushing  C  which  is  bored  straight  on  the 
inside  and  turned  to  a  taper  on  the  outside,  this  bushing  be- 
ing secured  to  the  spindle  with  a  Woodruff  key  so  that  it  is 
a  tight  fit.  On  the  outside,  bushing  C  is  turned  to  a  suitable 
taper  to  fit  bearing  box  D,  and  bushing  C  is  threaded  at  the 
lower  end  and  furnished  with  a  collar  E  which  provides  for 
maintaining  a  tight  fit  between  bushing  C  and  bearing  box 
D.  By  screwing  up  collar. E,  provision  is  made  for  taking 


TAKE-UP 
CLAMP  NUT 


Machinery 


Fig.    6.      Adjustable    Bronze    Spindle    Bearing    furnished    with 

Means   of   compensating    for    Wear   and    Provision    for 

Continuous    Lubrication   from    a    Reservoir 

up  any  wear  which  develops  in  this  bearing  after  the  ma- 
chine is  put  into  service.  It  will  be  apparent  that  the  use 
of  bushing  C,  which  is  keyed  to  the  spindle,  is  a  substitute 
for  having  the  journal  made  an  integral  part  of  the  spindle, 
as  it  is  at  the  lower  end.  The  reason  for  having  the  upper 
journal  in  the  form  of  a  bushing  keyed  to  the  spindle  is  that 
this  greatly  facilitates  the  work  of  assembling  the  machine. 
Collars  B  and  E  are  provided  with  split  nuts  to  hold  them 
in  place  ,after  making  the  settings. 

Provision  for  Cleaning  Bearings.  Fig.  6  shows  a  form  of 
spindle  bearing  construction  which  has  been  adopted  as  one 
of  the  standards  in  building  machine  tools  made  by  the  Gar- 
vin  Machine  Co.  It  will  be  apparent  from  the  illustration 


12 


PLAIN   BEARINGS 


that  in  working  out  this  design  provision  has  been  made  for 
supplying  the  bearing  with  lubricant  from  reservoir  A, 
which  extends  around  the  outside  of  the  bearing  box.  A 
supply  of  oil  is  delivered  into  this  reservoir  through  tube 
B  and  finds  its  way  from  the  reservoir  to  the  bearing  sur- 
face through  holes  which 
connect  with  oil-grooves 
cut  on  the  inside  of  the 
bearing  box.  The  reservoir 
is  cleaned  out  by  opening 
drain  pipe  C  to  allow  the 
dirty  oil  to  run  out,  after 
which  the  bearing  is  flush- 
ed with  kerosene  before 
closing  drain  C  and  filling 
the  reservoir  with  a  supply 
of  fresh  oil.  It  will  be  seen 
that  the  spindle  is  threaded 
on  the  straight  portion  di- 
rectly to  the  left  of  the  ta- 
pered journal,  to  provide 
for  drawing  the  spindle 
into  its  tapered  bearing  box 
when  it  becomes  necessary 
to  compensate  for  wear. 
Before  this  adjustment  can 
be  made,  soft  washer  G 
must  be  faced  off.  Collar 
D,  by  means  of  which  this 
adjustment  is  made,  is  split 

Machinery         at    °ne    S^Q    an(*    furnished 


Fig.    7.      Adjustable     Bearings    de- 

signed   for   Vertical    Spindle 

Profiling    Machine 


with  a  clamp  screw  E,  so 
that  when  the  bearing  has 
been  adjusted  to  obtain  the 
desired  fit,  screw  E  is  tightened  to  clamp  collar  D  firmly  in 
the  exact  position  to  which  it  has  been  set.  In  most  ma- 
chine tool  bearings,  provision  must  be  made  for  carrying  a 
thrust  load  in  addition  to  the  normal  radial  load  which 
comes  on  the  bearing.  In  the  present  case,  this  result  is 


PLAIN   BEARINGS 


13 


obtained  by  designing  the  spindle  with  a  flange  at  the  large 
end  of  the  taper.  This  flange  bears  against  two  hardened 
and  ground  washers  F  and  a  soft  washer  G,  which  are 
placed  between  the  flange  on  the  spindle  and  the  end  of  the 
tapered  bearing  box,  the  thrust  load  being  carried  in  this 
way  without  imposing  an  undue  strain  and  unnecessary 
amount  of  wear  on  the  bearing. 

In  Fig.  7  there  is  shown  the  form  of  adjustable  bronze 
bearings  which  are  used  for  carrying  the  vertical  spindle 
of  the  Nos.  2  and  4  profiling  machines  built  by  the  Garvin 
Machine  Co.  As  in  the  case  of  the  bearing  design  shown 
in  Fig.  6,  it  will  be  seen  that  provision  is  made  for  carrying 


Fig.  8.      Example  of  Bearing  Design  where  Compensation  for  Wear 
is    accomplished    by    compressing    the    Bronze    Bearing    Box 

the  thrust  load  by  having  a  flange  at  the  lower  end  of  the 
spindle  which  bears  against  an  arrangement  of  thrust 
washers.  These  washers  serve  the  double  purpose  of  tak- 
ing the  thrust  of  the  spindle  and  providing  means  of  com- 
pensating for  any  wear  and  lost  motion  which  may  develop 
in  the  lower  spindle  bearing. 

When  wear  in  the  bearing  must  be  compensated  for,  this 
is  done  by  facing  off  the  soft  thrust  washer  and  tightening 
collar  C',  which  is  carried  on  the  threaded  section  of  the 
spindle,  the  result  being  that  the  spindle  is  drawn  up  into 
the  tapered  bearing  box.  At  the  upper  end  of  the  spindle 
there  is  a  tapered  steel  bushing  E  which  is  keyed  to  the 
straight  end  of  the  spindle  with  a  Woodruff  key.  On  the 


14 


PLAIN   BEARINGS 


THRUST  WASHERS: 

HARDENED  STEEL 

AND  BRONZE 


outside,  bushing  E  is  machined  to  a  taper  to  fit  bronze  bear- 
ing box  F  accurately,  and  when  it  is  necessary  to  make  ad- 
justment to  compensate  for  wear,  threaded  collar  G  is  tight- 
ened. It  will  be  apparent  that  both  collars  C  and  G  are 
split  on  one  side  and  furnished  with  binding  screws  to  pro- 
vide for  securing  the  collars  in  the  desired  positions  after 
the  required  adjustment  has  been  made. 

Compensation  for  Wear  by  Compressing  Bearing  Box. 
In  Fig.  8  there  is  shown  a  different  method  of  providing 
compensation  for  wear  in  a  tapered  bronze  spindle  bearing 

box.  This  construc- 
tion is  used  on  the 
Garvin  No.  2  uni- 
versal milling  ma- 
chines. At  the  front 
end,  the  spindle  is  fur- 
nished with  a  bearing 
box  of  the  same  gen- 
eral design  as  those 
which  have  already 
been  described,  but  at 
the  rear  end,  as  will  be 
seen,  the  bronze  box  is 
split  and  fitted  to  the 
straight  end  of  the 
spindle,  this  box  being  tapered  on  the  outside  to  engage 
a  bushing  in  the  machine  frame  with  which  it  remains 
in  fixed  contact.  This  necessitates  an  entirely  different 
method  of  adjusting  the  box  to  afford  compensation 
for  wear,  and  such  adjustment  is  obtained  by  tighten- 
ing threaded  collar  A  to  provide  for  pulling  the  ta- 
pered bearing  box  into  the  bushing  in  the  machine  frame. 
When  this  collar  is  tightened  to  pull  the  bearing  box  into 
the  tapered  bushing,  the  bronze  box  is  compressed  against 
the  straight  journal  on  the  spindle,  thus  taking  up  any  wear 
which  may  have  developed.  Attention  is  also  called  to  oil- 
hole  B9  which  delivers  a  supply  of  oil  into  reservoir  C, 
formed  in  this  bearing  box  to  provide  a  liberal  supply  of 


Machinery 


Fig.     9.        Bearings     designed     so     that 
Compensation    for    Wear    is    accom- 
plished   by    drawing    Spindle 
into  Tapered    Box 


PLAIN   BEARINGS  15 

oil;  the  oil  flows  from  the  reservoir  through  oil-holes  con- 
necting with  grooves  machined  in  the  bearing  surface  of 
the  box  to  provide  for  distribution  of  lubricant  over  the 
bearing.  The  same  arrangement  of  an  oil-hole  and  oil 
reservoir  in  the  bearing  box  is  provided  at  the  front  end  of 
the  spindle. 

Compensation  for  Wear  by  Drawing  Spindle  into  Tapered 
Box.  Fig  9  shows  an  example  of  the  design  of  bearings  for 
a  machine  tool  spindle,  where  the  journals  are  directly  sup- 
ported by  tapered  bronze  boxes  at  both  ends.  It  will  be 
seen  that  at  the  front  end  of  the  spindle  (which  is  the  left- 
hand  end  in  this  case)  a  tapered  bronze  box  A  is  provided 
which  is  threaded  on  the  outside  at  both  ends.  To  compen- 
sate for  wear  which  may  develop  in  these  bearing  boxes,  the 
method  of  procedure  is  as  follows :  Threaded  collar  B,  car- 
ried at  the  right-hand  end  of  the  spindle,  is  tightened  to 
draw  the  entire  spindle,  and  hence  the  tapered  bearing  at 
this  end  of  the  spindle,  back  into  box  C  to  compensate  for 
any  lost  motion  which  may  have  developed  as  the  result  of 
wear.  When  this  result  has  been  obtained,  a  corresponding 
adjustment  must  be  made  on  box  A,  the  procedure  being  as 
follows :  Jam  nut  B  is  loosened  and  the  rear  step  plug  be- 
hind the  nut  is  slacked  away,  after  which  threaded  collar  D 
at  the  front  end  of  the  spindle  is  loosened  and  collar  E  is 
then  tightened  to  draw  the  front  tapered  bearing  box  up  to 
a  snug  fit  on  the  journal ;  this  also  pushes  the  entire  spindle 
back  into  the  rear  tapered  bearing  C.  When  this  result  has 
been  obtained,  collar  D  is  tightened  to  hold  the  box  in  ex- 
actly the  position  in  which  it  has  been  set.  Then  the  rear 
step  plug  is  carefully  adjusted  against  the  rear  end  of  the 
spindle  and  locked  by  a  jam  nut  B.  This  is  another  bear- 
ing design  used  by  the  Garvin  Machine  Co. 

Cast-iron  and  Babbitt  Spindle  Bearings.  Experience  has 
shown  that  very  satisfactory  service  is  obtained  from  a  hard 
steel  journal  running  in  a  cast-iron  bearing.  With  such  a 
combination,  it  is  found  that  the  cast  iron  has  a  tendency  to 
become  glazed  on  the  surface  in  such  a  way  that  the  co- 
efficient of  friction  between  the  bearing  and  its  journal  is 


16 


PLAIN  BEARINGS 


very  small,  thus  making  the  transmission  efficiency  of  the 
bearing  correspondingly  high ;  also  a  bearing  of  this  kind 
is  so  hard  that  wear  becomes  almost  a  negligible  quantity. 
In  Fig.  10  there  is  shown  a  type  of  spindle  bearing  con- 
struction which  has  been  adopted  as  a  standard  by  the  R. 
K.  LeBlond  Machine  Tool  Co.,  of  Cincinnati,  Ohio,  in  build- 
ing lathes,  milling  machines,  and  cutter  grinders.  This 
consists  of  a  cast-iron  box  at  the  front  end  and  a  babbitted 


Machinery 


Fig.    10.      Example   of   Spindle    Construction    used   for    Lathes, 

Milling    Machines,   and   Cutter  Grinders,  where    Front 

Bearing     is    of    Chilled     Cast     Iron    and     Rear 

Bearing    is    lined    with    Babbitt 

box  at  the  rear  end  of  the  spindle,  and  the  results  obtained 
by  this  combination  have  proved  so  satisfactory  in  practice 
that  a  detailed  description  will  be  of  interest. 

The  spindle  is  made  of  50-point  carbon  steel,  and  over 
this  there  is  pressed  at  the  front  end  a  hardened  steel  bush- 
ing made  of  Shelby  seamless  tubing.  In  making  this  bush- 
ing, the  blank  is  cut  off  and  annealed,  after  which  it  is 
bored,  turned,  and  carburized ;  then  it  is  necessary  to  round 
up  the  bushing  to  remove  any  distortion  which  has  been 


PLAIN   BEARINGS  17 

produced  during  the  heat-treatment,  after  which  it  is  re- 
heated and  quenched  in  water  to  make  it  glass-hard.  After 
hardening,  the  bushing  must  show  a  scleroscope  hardness 
of  80  degrees,  and  those  which  fail  to  fulfill  this  test  are 
heat-treated  again.  The  hardened  bushings  are  ground  on 
the  inside  and  rough-ground  on  the  outside,  after  which  they 
are  again  tested  for  hardness  before  being  pressed  on  the 
spindle.  The  fit  of  the  bushing  on  the  spindle  is  so  adjusted 
that  from  seven  to  ten  tons'  hydraulic  pressure  is  re- 
quired to  push  it  into  place,  after  which  the  bush- 
ing is  ground  to  standard  size.  The  cast  iron  for  the  bear- 
ing is  cast  against  a  chill  to  make  the  metal  dense 
and  close-grained.  Mention  has  already  been  made  of 
the  fact  that  this  hardened  steel  journal  is  carried 
in  a  cast-iron  bearing  box  which  is  an  integral  part  of  the 
main  headstock  casting.  This  eliminates  an  extra  joint  be- 
tween the  bronze  box  or  a  babbitt-lined  bearing,  and  affords 
a  more  rigid  construction,  although  the  work  of  scraping 
the  cast-iron  spindle  bearing  to  an  accurate  fit  and  perfect 
alignment  is  a  difficult  job,  calling  for  the  services  of  an  ex- 
perienced mechanic.  A  cast-iron  bearing  of  this  type  must 
be  more  accurately  finished  than  either  a  babbitted  or  a 
bronze-bushed  bearing,  because  no  dependence  can  be 
placed  upon  the  spindle  wearing  itself  to  a  satisfactory  fit 
after  the  machine  is  placed  in  service;  the  bearing  must 
fit  properly  before  the  machine  is  started.  Several  years 
ago  the  R.  K.  LeBlond  Machine  Tool  Co.  built  four  trial 
head-stocks  equipped  with  the  following  combinations  of 
journals  a  Ad  bearings:  (1)  Cast-iron  bearings  and  soft 
steel  spindle;  (2)  bronze  bearings  and  soft  steel  spindle; 
(3)  babbitted  bearings  and  soft  steel  spindle;  and  (4)  cast- 
iron  bearings  and  hardened  steel  spindle. 

Lathes  with  spindles  of  these  types  were  kept  in  constant 
use  on  work  of  the  same  general  character,  and  when  ex- 
amined, the  condition  of  the  hardened  steel  journal  running 
in  -a  cast-iron  box  was  found  to  be  the  best,  neither  the 
spindle  nor  the  box  being  worn  to  an  appreciable  extent 
and  the  grinder  and  scraper  marks  still  being  visible.  The 


18  PLAIN  BEARINGS 

combination  of  a  soft  steel  journal  and  bronze  box  was  in 
good  condition,  but  the  journal  was  slightly  ridged  in  the 
center.  The  soft  steel  spindle  in  a  cast-iron  box  was  ap- 
preciably worn,  but  the  soft  steel  spindle  in  a  babbitt  box 
was  in  first-class  condition.  There  are  lathes  in  the  Le 
Blond  shops  at  the  present  time  in  which  hardened  steel 
spindles  have  been  running  in  cast-iron  boxes  for  about 
twelve  years  without  any  adjustment  having  been  neces- 
sary. The  wear  is  so  slight  that  it  can  scarcely  be  meas- 
ured with  the  most  delicate  instruments.  It  is  very  im- 
portant, however,  to  have  the  combination  of  a  hardened 
steel  spindle  and  cast-iron  box,  as  a  soft  steel  spindle  and  a 
cast-iron  box  is  much  less  satisfactory  than  a  soft  steel 
spindle  and  either  a  bronze-bushed  or  babbitted  bearing. 

At  the  rear  end,  the  spindle  of  LeBlond  lathes,  milling 
machines,  or  cutter  grinders  is  supported  in  a  babbitted 
bearing.  It  will  be  seen  that  the  seat  for  this  babbitted 
bearing  is  dovetailed  and  the  babbitt  is  poured,  after  which 
the  bearing  is  bored  in  position.  No  attempt  is  made  to 
peen  the  metal.  Experience  has  shown  that  wear  on  the 
back  bearing  in  a  headstock  of  this  construction  is  propor- 
tionate to  the  wear  of  the  front  box  with  its  hardened  steel 
journal  running  in  a  cast-iron  bearing.  Practically  no  at- 
tention is  required  by  bearings  of  this  form  after  the  front 
bearing  has  run  for  a  sufficient  time  to  enable  the  cast  iron 
to  become  glazed.  The  metal  becomes  so  hard  on  the  sur- 
face that  it  can  scarcely  be  "touched"  with  a  scraper. 

Oilless  Bearings.  The  advantages  of  the  oilless  or  self- 
lubricating  bearing  for  many  classes  of  service  have  led  to 
the  development  of  several  different  types,  each  of  which 
doubtless  has  its  advantages  when  applied  under  suitable 
conditions.  One  type  consists  of  wood  impregnated  with 
wax,  oil  or  paraffin.  Another  is  made  of  bronze  and  has 
graphite  inserts.  Still  another  type  is  formed  of  graphite 
impregnated  with  some  bearing  metal  such  as  a  white  metal 
alloy  or  bronze. 

One  type  of  "oilless"  bearing  has  on  the  bearing  surface, 
symmetrical  grooves  of  various  designs,  depending  upon 


PLAIN  BEARINGS  19 

the  service  for  which  the  bushing  is  intended.  These 
grooves  are  packed  solid  by  means  of  hydraulic  pressure 
with  a  special  hard  graphite  lubricant.  When  the  bush- 
ings are  once  installed  and  in  use,  fine  particles  of  the 
graphite  lubricant  are  distributed  over  the  entire  bearing 
surface  of  the  bushing.  Ample  lubrication  is  provided  for 
almost  any  form  of  bearing  contact,  whether  the  movement 
be  oscillating,  vertical,  horizontal,  or  full  revolution.  Ow- 
ing to  the  scientific  design  of  the  graphite  grooves  which 
fits  them  for  the  particular  service  required,  wear  is  re- 
duced to  a  minimum.  The  design  of  the  graphite-packed 
grooves  varies  in  different  bushings  because  some  bush- 
ings are  subjected  to  different  kinds  of  contact  from  others. 
These  bushings  are  suitable  for  use  in  machine  tools,  coun- 
tershafts, lineshaft  hangers,  electric  motors,  etc.,  but,  al- 
though they  are  styled  "oilless"  bearings,  it  is  recom- 
mended that  about  25  per  cent  of  the  volume  of  oil  which 
would  be  required  to  operate  efficiently  an  ordinary  plain 
bearing  of  the  same  size  should  be  applied  to  these  oilless 
bearings.  However,  in  the  event  of  failure  on  the  part  of 
the  attendant  to  give  the  bearing  the  required  oil,  this  lack 
of  attention  is  not  so  likely  to  result  disastrously,  as  would 
be  the  case  with  an  ordinary  bronze-bushed  bearing. 

Another  type  of  oilless  bearing  consists  of  a  bushing 
made  of  either  hard  maple  or  iron  wood,  which  is  thor- 
oughly impregnated  with  a  mixture  of  graphite  and  other 
lubricant  by  a  special  treatment.  These  are  more  truly 
"oilless"  bearings  than  the  type  that  has  graphite  inserts, 
because  when  the  bearing  is  in  operation  a  slight  increase 
in  temperature  resulting  from  friction  causes  the  bearing 
to  exude  some  of  the  lubricant  with  which  it  has  been  im- 
pregnated, thus  providing  for  efficient  transmission  of 
power.  These  bearings  are  especially  adapted  for  use  in 
loose  pulleys ;  and  in  many  cases  they  are  run  without  any 
provision  for  lubrication.  Some  users  prefer  to  drill  the 
usual  oil-hole  in  the  hub  of  the  pulley  and  in  the  bushing, 
so  that  a  little  oil  can  be  added  from  a  squirt  can,  and  very 
satisfactory  results  were  obtained  where  the  bushings  were 


20  PLAIN   BEARINGS 

used  in  this  way.  They  must  be  properly  supported  to  pre- 
vent splitting,  although  with  sufficient  support  these  wood- 
en bushings  have  ample  strength  to  resist  any  crushing 
load  to  which  they  will  be  subjected  when  used  in  loose 
pulleys  and  similar  positions. 

Still  another  type  of  oilless  bearing  consists  of  graphite 
bushings  made  of  the  required  sizes,  and  impregnated  with 
white  metal  or  bronze  to  produce  what  is  known  as  "graph- 
alloy."  The  metal  used  for  impregnating  the  graphite  de- 
pends upon  the  class  of  work.  All  parts  such  as  shaft  bear- 
ings are  impregnated  with  a  white-metal  alloy  or  babbitt 
metal  of  special  composition.  The  parts  used  in  connec- 
tion with  electrical  apparatus  are  impregnated  with  a  cop- 
per alloy  which  is  also  utilized  for  such  parts  as  steam  tur- 
bine packing  rings,  etc.,  which  must  withstand  high  steam 
temperatures.  The  use  of  copper  for  the  electrical  work  is 
essential  because  of  its  electrical  conductivity. 

The  extent  to  which  the  graphite  is  impregnated  with 
the  metal  is  indicated  by  the  fact  that  the  weight  of  the 
graphite  is  0.057  pound  per  cubic  inch,  whereas  the  weight 
of  the  metalized  product  is  0.145  pound  per  cubic  inch 
when  impregnated  with  babbitt,  the  increase  of  weight 
due  to  the  metallizing  process  being  practically  150  per 
cent.  The  metal  in  "graphalloy"  is  about  60  per  cent  by 
weight,  or  25  per  cent  by  volume.  The  specific  gravity  is 
4  and  the  compressive  strength,  approximately  14,000 
pounds  per  square  inch.  "Graphalloy"  is  not  injured  by 
the  application  of  lubricant.  In  fact,  the  use  of  an  applied 
lubricant  is  recommended  when  the  bearings  are  used  for 
rather  heavy  service. 

At  the  present  time  "graphalloy"  in  the  form  of  bear- 
ings is  applied  to  light-duty  machinery  operating  at  high 
speeds  and  to  heavier  service  when  the  speeds  are  relatively 
low.  Its  use  is  recommended  particularly  where  the  appli- 
cation of  oil  is  either  objectionable,  difficult,  or  likely  to  be 
neglected.  These  bearings  are  commonly  applied  to  loose 
pulleys,  vertical  shaft  bearings,  conveyors,  textile  machin- 


PLAIN   BEARINGS  21 

ery,  canning  machinery,  etc.  They  are  recommended  for 
loose  pulleys  in  cotton  and  silk  mills  and  have  also  been 
utilized  successfully  on  paper  machinery,  shoe  machinery, 
wrapping  machines,  cotton  spinning  frames,  etc.,  which  op- 
erate on  a  product  that  may  be  damaged  by  the  use  of  oil 
One  of  the  important  uses  is  for  vertical  bearings,  such  as 
are  found  on  governors,  fans,  etc.  The  use  of  "graphalloy' 
is  not  recommended  where  the  combination  of  speed  and 
pressure  is  excessive.  As  a  general  rule,  a  bearing  pres- 
sure of  50  pounds  per  square  inch  of  projected  area  should 
not  be  exceeded.  The  limitations  of  this  material  are  indi- 
cated by  the  following  rule  which  applies  to  a  bearing  used 
without  a  lubricating  oil :  The  surface  speed  of  the  shaft 
in  feet  per  second  multiplied  by  the  pressure  in  pounds  per 
square  inch  on  the  projected  bearing  area  should  not  ex- 
ceed a  constant  of  about  200.  The  temperature  of  "graph- 
alloy"  bearings  is  somewhat  higher  than  that  of  ordinary 
bearings  lubricated  with  oil  which  is  principally  due  to  the 
fact  that  "graphalloy"  is  a  relatively  poor  conductor  of  heat. 
As  soon  as  a  "graphalloy"  bearing  is  put  into  service,  a 
graphite  coating  begins  to  form  on  the  shaft,  the  thickness 
of  the  coating  depending  upon  the  smoothness  of  the  shaft. 
This  coating  soon  becomes  very  smooth  and  hard,  which 
greatly  reduces  the  coefficient  of  friction  and  the  tempera- 
ture of  the  bearing.  It  is  claimed  that  a  temperature  as 
high  as  200  or  300  dgrees  F.  will  not  injure  the  bearing 
or  cause  it  to  seize  the  shaft.  The  temperatures  are  mod- 
erate at  high  speeds,  provided  the  bearing  pressure  is  low. 
On  the  other  hand,  if  the  bearing  pressure  is  relatively 
high  and  the  speed  low  or  moderate,  the  temperature  will 
also  be  low. 

Thrust  Bearings.  Thrust  bearings  are  of  two  very  gen- 
eral classes:  ste&^bearings  and  collar  bearings.  In  step 
bearings,  the  mrust  is  taken  by  the  end  of  the  supporting 
shaft;  in  collar  bearings,  by  projections^ or  shoulders.  The 
simplest  kind  of  a  thrust  bearing  is  the  pivot  bearing,  ex- 
emplified by  the  bearings  for  watch  pinions  and  by  a  lathe 


22  THRUST  BEARINGS 

center  taking  the  end-thrust  of  a  cut  on  a  piece  held  be- 
tween the  centers.  In  general,  however,  the  end-thrust  is 
taken  by  a  large  flat  or  nearly  flat  surface.  When  this  is 
the  case,  several  considerations  present  themselves  which 
must  be  given  due  attention  by  the  machine  designer.  As- 
sume that  the  flat  end  of  a  vertical  cylindrical  shaft  carry- 
ing a  weight  or  otherwise  subjected  to  pressure  is  sup- 
ported by  a  flat  surface.  Then,  if  the  shaft  rotates,  the 
velocities  of  points  on  its  end  surface  at  different  radial 
distances  from  its  axis,  will  vary.  The  velocities  of  the 
points  near  the  outside  will  be,  in  comparison,  very  high, 
while  the  velocity  of  a  point  near  the  center  will  be  low. 
On  account  of  this  variation  in  velocity,  the  wear  on  the 
end  surface  of  the  shaft  and  the  thrust  surface  of  the  bear- 
ing will  be  considerably  uneven.  If  the  parts  are  well  fit- 
ted together  when  new,  so  that  a  uniform  pressure  is  pro- 
duced all  over  the  end  of  the  shaft  and  bearing,  then  the 
outer  parts  of  the  bearing  surfaces  will  wear  away  most 
rapidly.  This  again  increases  the  pressure  at  the  center, 
which  sometimes  may  become  so  intense  as  to  exceed  the 
ultimate  crushing  strength  of  the  material.  The  unequal 
wear  of  the  surfaces  of  thrust  bearings  is  one  of  the  most 
difficult  problems  meeting  the  designer  of  machinery  of 
which  such  bearings  form  a  part. 

The  Schiele  Curve.  Experiments  carried  out  by  Schiele 
show  that  the  wear  is  theoretically  along  a  curve  called  the 
tractrix.  If  an  end-thrust  bearing  is  made  of  a  form  cor- 
responding to  the  Schiele  curve  then  the  wear  in  the  direc- 
tion of  the  axis  of  the  thrust  shaft  will  be  uniform  at  all 
points;  but  while  this  curved  form  would  be  theoretically 
correct  it  has  been  shown  in  practice  that  nothing  is  to  be 
gained  by  the  use  of  bearings  having  this  complicated 
shape. 

Simple  Step  Bearings  for  Light  Duty.  For  light  duty, 
simple  step  bearings  of  the  types  shown  in  Figs.  11  to  14 
meet  the  requirements.  The  intense  pressure  at  the  center 
and  the  consequent  unequal  wear  are  partly  avoided  in  the 


THRUST   BEARINGS 


23 


bearing  in  Fig.  11  by  cutting  away  the  metal  at  the  center 
of  the  shaft,  as  shown,  leaving  an  annular  ring  which  takes 
the  thrust.  This  procedure  is  advisable  in  all  step  bear- 
ings. Another  difficulty  met  with  in  bearings  of  this  type 
is  the  question  of  lubrication.  If  the  speed  of  the  shaft  is 
high,  the  centrifugal  force  tends  to  throw  the  oil  out  from 
the  center.  Special  provisions  must  then  be  made  for  again 
returning  the  oil  to  the  center,  as  otherwise  the  bearing 
would  wear  down  rapidly,  become  heated,  etc.  In  Fig.  11, 
a  simple  method  is  shown  for  automatically  returning  the 
oil  to  the  bearing  surfaces.  An  oil-passage  is  made  from 


Machinery,  N.  Y. 


Figs.    11    and    12.      Simple    Designs    of   Step    Bearings 

the  chamber  A  formed  around  the  shaft  to  the  center  of  the 
shaft  at  the  bottom.  When  the  channel  and  chamber  are 
once  filled  with  oil,  this  oil  will  continue  to  circulate  auto- 
matically; it  will  be  drawn  in  at  the  bottom,  be  thrown 
outward  by  the  centrifugal  force,  find  its  way  into  the 
chamber  A,  and  finally,  through  the  channel,  return  to  the 
center  of  the  bearing. 

When  a  bearing  for  heavier  duty  is  required,  the  design 
shown  in  Fig.  12  is  quite  commonly  adopted.  A  number 
of  disks  or  washers  are  placed  between  the  end  of  the 
thrust  shaft  and  the  supporting  bearing,  in  order  to  intro- 
duce a  number  of  wearing  surfaces,  instead  of  having  the 


24  THRUST  BEARINGS 

end  of  the  shaft  and  the  box  take  all  the  wear.  Due  to  the 
fact  that  the  series  of  washers  introduced  permits  of  a 
lower  speed  between  each  pair  of  washers,  the  wear  is 
quite  materially  reduced.  Should  the  pressure  cause  any 
two  washers  to  heat  and  bind,  the  frictional  resistance 
between  them  ceases,  as  one  washer  is  free  to  follow  the 
motion  of  the  other,  and  the  oil  will  have  an  opportunity  to 
get  between  the  surfaces  and  cool  them  off. 

A  hole  may  be,  and  generally  is,  drilled  through  the 
centers  of  the  washers,  as  shown  in  Fig.  12,  and  the  same 
method  for  continual  lubrication,  as  shown  in  Fig.  11,  may 
be  used  to  advantage.  Every  alternate  washer  is  com- 
monly made  of  hardened  tool  steel  or  case-hardened  ma- 
chine steel,  while  the  others  are  made  of  bronze.  This  com- 
bination provides  for  good  wearing  qualities.  If  the  thrust 
shaft  is  made  of  soft  machine  steel,  and  the  box  of  cast 
iron,  the  top  washer  is  often  secured  to  the  shaft,  and  the 
bottom  washer  to  the  box,  so  that  all  the  wear  may  be 
concentrated  upon  the  washers,  which  can  easily  be  re- 
placed. 

In  Fig.  13  is  shown  an  improvement  on  the  bearing  in 
Fig.  12.  This  construction  is  recommended,  in  particular, 
in  cases  where  the  shaft  and  its  bearing  box  cannot  be 
properly  aligned  with  one  another.  The  washers  have 
spherical  faces,  being  alternately  convex  and  concave.  They 
are  slightly  smaller  in  diameter  than  the  bearing  box  into 
which  they  are  inserted,  so  that  they  may  have  an  oppor- 
tunity to  adjust  themselves  to  a  perfect  bearing  on  each 
other,  and  thereby  make  up  for  the  differences  in  the  align- 
ment of  the  thrust  shaft  and  bearing  box. 

Another  type  of  thrust  bearing  for  loads  which  are  not 
excessive  is  shown  in  Fig.  14.  It  is  a  well  established  prin- 
ciple that  it  is  better  to  take  thethrust  j)f  ajbearing^as  near 
the  center  of  the  shaft  as  the  load  to  be  carried  will  allow^. 
The  farther  away  from  the  center  the  support  is,  the  great- 
er is  the  motion  and  the  greater  is  the  retarding  effect  of  the 
friction.  The  thin  convex  washers  used  are  of  tool  steel, 


THRUST  BEARINGS 


25 


hardened,  and,  although  the  bearing  between  them  is  very 
small,  their  strength  and  hardness  is  such  that  they  are 
capable  of  standing  a  considerable  pressure,  although  not 
so  great  a  one,  probably,  as  the  other  forms  shown  in  Figs. 
11,  12,  and  13.  In  this  bearing,  also,  there  is  no  difficulty 
in  keeping  the  surfaces  well  oiled,  since  all  that  is  neces- 
sary is  to  keep  the  chamber  well  flooded  with  oil. 

As  already  mentioned,  flat  thrust  bearings  should  be 
made  of  an  annular  form.  It  is  good  practice  to  make  the 
inside  diameter  one-half  of  the  external  diameter.  Experi- 
ments made  on  flat  pivot  thrust  bearings,  three  inches  in 


Machinery, N,Y. 


Figs.  13  and  14.     Other  Designs  of  Step   Bearings 

diameter,  indicate  that  the  coefficient  of  friction  between 
a  steel  pivot  and  a  manganese-bronze  bearing,  properly 
lubricated,  using  two  radial  oil  grooves  only,  varies  from 
0.018  at  50  revolutions  per  minute,  to  an  average  of  0.011 
at  350  revolutions  per  minute.  If  four  radial  oil  grooves 
are  used  instead  of  two,  the  friction  is  approximately 
doubled,  due  to  rupture  of  the  oil  film. 

Load  on  Thrust  Bearings.  The  load  that  may  be  safely 
carried  by  a  thrust  bearing  varies  with  the  velocity  of  the 
rubbing  surfaces.  The  accompanying  table  may  be  used 
as  a  guide  in  designing  bearings  in  which  the  shaft  is  made 
from  wrought  iron  or  steel  and  the  bearing  from  bronze  or 


26 


THRUST   BEARINGS 


brass,  and  which  have  ample  lubrication.  In  general,  it  is 
possible  to  use  bath  lubrication  for  thrust  bearings,  that  is, 
the  running  surfaces  are  submerged  constantly  in  a  bath 
of  oil.  If  the  shaft  is  made  from  cast  iron  running  on 
bronze  or  brass  bearings,  the  values  in  the  table  for  allow- 
able pressure  should  be  only  one-half  of  those  given.  In 
designs  where  the  motion  is  slow  and  heating  cannot  well 
result,  as  in  pivots  for  swing  bridges  and  similar  construc- 
tions, pressures  up  to  4000  pounds  per  square  inch  are  per- 
missible. 


Allowable  Pressure,  in  Pounds  per  Square  Inch,  on 
Thrust  Bearings 


Average   Velocity   of 
Rubbing    Surface, 
Feet  per  Minute 

Safe  Pressure, 
Pounds 
per  Sq.  In. 

Average    Velocity   of 
Rubbing    Surface, 
Feet  per  Minute 

Safe  Pressure, 
Pounds 
per  Sq.  In. 

Slow  and  Intermittent 
50 
50  to  100 

1500 
200 
100 

100  to  150 
150  to  200. 
Over  200 

75 
60 
50 

Collar  Thrust  Bearings.  In  collar  thrust  bearings,  the 
thrust  is  taken  by  projections  or  shoulders  on  the  shaft, 
often  at  some  distance  from  its  end.  This  type  of  bearing 
is  used  when  a  greater  thrust  than  can  be  conveniently 
placed  on  a  single  flat  or  step  bearing  is  to  be  taken  care 
of.  In  a  well-made  bearing,  each  of  the  collar  surfaces 
takes  its  proportionate  part  of  the  load,  and  it  is  thus  pos- 
sible, without  using  excessive  diameters,  to  distribute  prop- 
erly a  very  great  thrust  on  a  number  of  collars  formed 
solidly  with  the  shaft  by  cutting  a  number  of  grooves  in  the 
latter.  One  advantage  of  the  collar  bearing  is  that  the  dif- 
ference between  the  outer  and  inner  diameters  of  the  bear- 
ing surface  is  not  very  great,  and  hence  the  velocities  at  the 
outer  and  inner  edges  do  not  vary  appreciably ;  this,  again, 
eliminates  unequal  wear  on  the  thrust  collar  surfaces.  The 
safe  load  that  may  be  placed  on  collar  thrust  bearings 
varies  between  60  to  100  pounds  per  square  inch. 

Collar  thrust  bearings  are  commonly  designed  with  spe- 
cial thrust  washers  let  into  the  bearing  proper,  these  thrust 


THRUST  BEARINGS  27 

washers  bearing  against  the  collars  on  the  shaft.  The  outer 
diameters  of  the  collars  are  usually  made  not  more  than 
one  and  one-half  times  the  diameter  of  the  shaft.  In  the 
case  of  small  bearings  of  cheaper  design,  the  bearing  sur- 
faces of  the  thrust  bearings  are  sometimes  made  integral 
with  the  bearing  itself,  but  this  design  is  not  to  be  recom- 
mended, as  it  is  difficult  to  distribute  the  load  evenly  be- 
tween the  different  collars.  When  the  main  casting  is 
made,  say,  of  cast  iron,  and  bearing  washers  of  brass  are 
inserted,  it  is  possible  to  scrape  each  of  these  washers  until 
the  shaft  collars  bear  properly  against  each  washer,  so  that 
the  thrust  is  uniformly  distributed.  In  some  cases,  the 
bearing  washers  are  made  in  the  shape  of  a  horseshoe  fit- 
ted over  the  shaft,  so  that  each  washer  can  be  removed 
without  disturbing  the  bearing  or  the  shaft. 

Hydraulically  Supported  Step  Bearings.  The  type  of 
thrust  bearing  which  is  hydraulically  supported  has  very 
little  frictional  resistance  and  is  adapted  to  heavy  pres- 
sures and  high  speeds.  Bearings  of  this  type  which  have 
been  applied  to  Curtis  vertical  steam  turbines  are  so  de- 
signed that  oil  (water  may  also  be  used  with  this  type  of 
bearing)  under  sufficient  pressure  to  sustain  the  load,  is 
forced  between  the  recessed  plates  at  the  bottom  of  the 
shaft  and  then  passes  out  radially  in  the  form  of  a  thin  film 
and  up  through  a  cylindrical  guide  bearing  located  just 
above  the  bottom  plates,  thus  floating  the  shaft  upon  the 
oil  film. 

Thrust  Bearing  Design  Based  on  Principle  of  Wedge- 
shaped  Oil  Film.  The  investigations  of  Professor  Osborne 
Reynolds,  following  the  experiments  of  Tower  on  well- 
fitted  car  journals  and  brasses  flooded  with  oil,  showed  that 
the  oil,  because  of  its  viscosity  and  adhesion  to  the  journal, 
is,  by  the  journal  rotation,  dragged  into  a  wedge-shaded 
space  between  the  journal  and  brass.  This  action  sets  up 
pressure  in  the  oil  film  which,  in  turn,  supports  the  load, 
thus  separating  the  bearing  surfaces.  The  design-jof-the 
Kingsbury  thrust  bearing is  based _jm-thi&  principle,  the 
bearing  floating  the  load  on  wedge-shaped  oil  films  which 


28  THRUST  BEARINGS 

form  automatically  and  without  employing  a  high  pressure 
oil  pump.  There  is  usually  a  flat  annular  revolving  plate 
with  the  bearing  face  immersed  in  oil  and  supported  on  one 
or  more  shoes  which  are  mounted  to  tilt  as  required  by  run- 
ning conditions.  These  bearings  are  made  for  both  hori- 
zontal and  vertical  shafts.  The  low-speed  bearings  may  be 
loaded  to  1000  pounds  or  more  per  square  inch  when  using 
heavy  oil  and  high-speed  bearings  with  light  oils  regularly 
carry  loads  up  to  500  pounds  per  square  inch.  The  friction 
loss  in  this  bearing  is  very  low.  According  to  an  approxi- 
mate rule  for  vertical  bearings  having  six  shoes  with  the 
inside  diameter  one-half  the  outside  diameter  and  loaded 
to  350  pounds  per  square  inch  of  shoe  area,  the  mean  co- 
efficient of  friction  is  0.00009  times  the  square  root  of  the 
revolutions  per  minute  and  varies  inversely  as  the  square 
root  of  the  unit  pressure,  when  using  dynamo  oil  having  a 
temperature  of  about  40  degrees  C.  The  coefficient  of  fric- 
tion has  been  found  by  a  large  number  of  tests  to  vary  be- 
tween 0.0008  and  0.003. 


CHAPTER    II 
BEARING   METALS 

BEARINGS  are  usually  composed  of  alloys  of  copper,  lead, 
tin,  antimony,  and  zinc,  and  are  known  as  babbitt  metal 
(after  the  name  of  the  discoverer  of  this  material),  white 
metal,  brass,  phosphor-bronze,  and  various  other  trade 
names.  Quite  a  number  of  these  are  patented,  such  as 
"plastic  bronze,"  etc.,  but  many  are  sold  merely  under  trade 
names,  and,  in  some  instances,  are  of  uncertain  compo- 
sition. The  combinations  of  the  metals  enumerated,  that 
are  used  for  bearing  purposes,  may  be  grouped  under  the 
two  heads  of  white  metal  and  bronze.  Bronze  is  the  term 
which  was  originally  applied  to  alloys  of  copper  and  tin  as 
distinguished  from  the  brasses,  or  alloys  of  copper  and 
zinc;  but  gradually  this  term  has  become  applied  to  nearly 
all  copper  alloys  containing  not  only  tin,  but  lead,  zinc,  etc., 
and  no  sharp  lines  of  demarcation  exist  between  the  two. 
Thus  white  metals  are  made  up  of  various  combinations  of 
lead,  antimony,  tin,  copper,  and  zinc,  and  may  contain  as 
few  as  two  elements,  or  all  five.  Bronzes  are  made  up  of 
combinations  of  copper,  tin,  lead,  and  zinc,  all  of  them  con- 
taining copper  and  one  or  more  of  the  other  elements. 

The  essential  characteristics  to  be  considered  in  any  alloy 
for  bearings  are  composition,  structure,  friction,  tempera- 
ture of  running,  wear  on  bearing,  wear  on  journal,  com- 
pressive  strength,  and  cost. 

It  is  impossible  to  have  one  alloy  reach  perfection  in  all 
of  these  requirements,  and  so  it  is  important  to  study  the 
possible,  compositions  and  determine  for  what  purpose  each 
is  adapted.  It  has  been  shown  that  a  bearing  should  be 
made  up  of  at  least  two  structural  elements,  one  hard  con- 
stituent to  support  the  load  and  one  soft  constituent  to  act 


30  BEARING   METALS 

as  a  plastic  support  for  the  harder  grains.  Generally  speak- 
ing, the  harder  the  surfaces  in  contact,  the  lower  the  co- 
efficient of  friction,  and  the  higher  the  pressure  under 
which  "seizure"  takes  place.  Consequently,  the  harder  the 
alloy  the  better.  A  hard,  unyielding  alloy  for  successful 
operation  must,  however,  be  in  perfect  adjustment,  a  state 
of  affairs  unattainable  in  the  operation  of  rolling  stock. 
For  this  reason,  the  lead-lined  bearing  was  introduced,  and 
the  practice  of  lining  bearings  has  now  become  almost  uni- 
versal. 

Comparison  between  Hard  and  Soft  Alloys  for  Bearings. 
While  the  harder  the  metals  in  contact  the  less  the  friction, 
there  will  also  be  the  greater  liability  of  heating,  because 
of  the  lack  of  plasticity  or  ability  to  mold  itself  to  conform 
to  the  shape  of  the  journal.  A  hard,  unyielding  metal  will 
cause  the  concentration  of  the  load  upon  a  few  high  spots, 
and  so  cause  an  abnormal  pressure  per  square  inch  on  such 
areas,  and  produce  rapid  abrasion  and  heating.  The 
bronzes  will  operate  with  less  heat  than  softer  composi- 
tions, while  the  softer  metals  will  wear  longer  than  the 
harder  metals.  In  the  matter  of  wear  of  journals,  how- 
ever, the  soft  metals  are  more  destructive.  Particles  of 
grit  and  steel  seem  to  become  imbedded  in  the  softer  metal, 
causing  it  to  act  upon  the  harder  metal  of  the  journal  like 
a  lap.  High-priced  compositions  are  used  that  have  but  lit- 
tle resistance  to  wear  compared  with  cheaper  compositions, 
and  low-priced  alloys  are  in  service  that  are  not  cheap  at 
any  price.  It  is  generally  conceded  that  soft  metal  bear- 
ings cause  a  marked  decrease  in  the  life  of  the  journal,  and 
yet  they  have  many  marked  advantages. 

Principal  Requirements  of  Bearing  Metals.  The  principal 
qualities  which  a  good  bearing  metal  should  have  are  good 
anti-ffictional  properties,  so  as  to  withstand  heavy  loads 
at  high  speed,  without  heating,  and  sufficient  compressive 
strength  so  as  not  to  be  squeezed  out  of  place  under  high 
pressure,  or  crack  or  break  when  subjected  to  sudden 
shocks.  In  addition  to  these,  many  other  properties  must 
be  considered  in  a  choice  of  bearing  metals  depending  upon 


BEARING   METALS  31 

the  special  purpose  for  which  the  material  is  to  be  utilized. 
Temperature  variation  is  often  an  important  factor,  espe- 
cially in  refrigerating  plants,  and  the  coefficient  of  expan- 
sion should  be  considered  to  prevent  undue  binding,  with 
consequent  destruction  of  the  bearing,  and  the  possible 
variation  in  other  properties,  such  as  brittleness,  ductility, 
etc.,  under  various  temperature  conditions.  In  addition, 
many  bearings  must  operate  under  conditions  where  they 
are  subject  to  chemical  action,  whether  that  of  brine  or 
ammonia  in  refrigerating  plants,  or  acids,  alkalies,  etc., 
in  chemical  establishments,  and  in  dynamo  and  motor  con- 
struction and  operation,  the  electrical  conductivity  must  be 
considered  as  well.  This  statement  applies  equally  to  all 
bearings  incorporated  in  electrical  machinery,  where  these 
must  serve  as  electrical  conductors,  such  as  the  bearings 
for  the  wheels  in  trolley  cars,  etc. 

The  chief  properties  which  have  been  developed  to  a 
greater  extent  than  others  in  machine  design  are  those  of 
friction  elimination  and  resistance  to  compressive  loads. 
Theoretically,  all  metals  have  the  same  friction,  according 
to  Thurston,-  and  the  value  of  the  soft  white  alloys  for 
bearings  lies  chiefly  in  their  ready  reduction  to  a  smooth 
surface  after  any  local  impairment  of  the  surface.  Under 
these  circumstances,  the  soft  alloys  flow  or  squeeze  from 
the  pressure,  forming  a  larger  area  for  the  distribution  of 
the  pressure,  thus  diminishing  its  amount  per  unit  of  area. 
Further,  the  larger  the  area  over  which  the  pressure  is 
extended,  the  less  becomes  the  liability  to  overheating  and 
consequent  binding.  Thus  the  frictional  properties  of  a 
bearing  are  in  inverse  ratio  to  their  compressive  resistance, 
and  invariably  the  best  bearing  alloys,  from  a  high  speed 
standpoint,  are  unsatisfactory  for  utilization  in  heavy  ma- 
chinery. The  introduction  of  an  iron  or  steel  grid  to  form 
the  base'  of  the  main  bearing,  and  to  be  filled  with  much 
softer  bearing  metals  than  could  ordinarily  be  used,  or  in 
some  cases  even  graphite,  is  a  step  in  the  right  direction, 
and  presents  possibilities  of  great  importance  in  this  field 
of  machine  development. 


32  BEARING   METALS 

Metals  Used  in  Bearing  Alloys.  Lead  flows  more  easily 
under  pressure  than  any  of  the  common  metals,  hence  it 
has  the  greatest  anti-frictional  properties.  A  number  of 
metals  exceed  lead  in  this  property,  but  their  cost  or  some 
other  factor  render  them  unavailable.  Lead  is  the  cheapest 
of  the  metals,  except  iron;  the  comparative  prices  of  the 
metals  used  in  bearing  alloys,  under  normal  conditions 
(previous  to  the  war),  were  -about  in  the  following  order 
per  one  hundred  pounds:  Lead,  $4;  zinc,  $5;  antimony, 
$9 ;  copper,  $13 ;  and  tin,  $30  or  more.  It  can  thus  be  seen 
that  the  more  lead  that  is  used  in  a  given  bearing,  the  soft- 
er it  is,  the  less  friction  it  possesses,  and  the  cheaper  it  can 
be  furnished.  It  is,  however,  too  soft  to  be  used  alone,  as 
it  cannot  be  retained  in  the  recesses  of  the  bearing  even 
when  used  simply  as  a  liner  and  run  into  a  shell  of  brass, 
bronze,  gun-metal,  or  some  other  alloy.  Various  other 
metals  have  been  alloyed  with  it,  such  as  tin,  antimony, 
copper,  zinc,  iron,  and  a  number  of  non-metallic  compounds, 
such  as  sodium,  phosphorus,  carbon,  etc.,  and  the  effect  of 
the  different  ingredients  is  now  fairly  well  understood. 

Alloys  Containing  Antimony.  If  antimony  is  added  to  the 
lead,  it  increases  its  hardness  and  brittleness,  and  if  tin  is 
added  as  well,  it  makes  a  tougher  alloy  than  lead  or  anti- 
mony alone.  Nearly  all  of  the  various  babbitt  metals  on  the 
market  are  alloys  of  lead,  tin,  and  antimony  in  various  pro- 
portions, with  or  without  other  ingredients  added.  In  such 
babbitts,  the  wear  increases  with  the  antimony  and  the 
price,  with  the  tin.  The  higher  antimony  babbitts  are  used 
in  heavy  machinery,  as  they  are  harder,  while  those  low  in 
antimony  are  used  in  high-speed  machinery.  The  steady 
increase  in  speed  at  which  various  operating  units  are  main- 
tained is  responsible  for  a  wide  deficiency  in  this  field  in 
the  duty  performed  by  the  bearing  metal.  The  chief  dif- 
ficulty at  present,  in  the  operation  of  the  modern  turbine, 
is  undoubtedly  the  maintenance  of  satisfactory  bearing  sur- 
faces. Soft  babbitts  have  never  sufficient  strength  to  sus- 
tain the  weight  and  shock  of  heavy  machinery  bearings  and, 
can  be  used  only  as  liners.  The  tendency  to  increase  in 


BEARING   METALS  33 

speed  as  well  as  in  weight  or  size  of  machinery  is  limited 
simply  by  the  satisfactory  operation  of  the  bearing  metal 
itself. 

Alloys  of  Lead  and  Antimony.  Lead  and  antimony  will 
alloy  in  any  proportion.  With  an  increase  in  antimony,  the 
alloy  becomes  harder  and  more  brittle.  It  has  been  deter- 
mined that,  when  it  is  made  of  13  parts  of  antimony  and  87 
parts  of  lead,  the  composition  will  be  of  homogeneous  struc- 
ture. If  there  is  a  greater  proportion  of  antimony,  free 
crystals  of  antimony  will  appear,  imbedded  in  the  composi- 
tion; and,  if  less  than  13  per  cent,  there  appear  to  be  grains 
of  the  mixture  itself  imbedded  in  the  lead  as  the  body  sub- 
stance. According  to  a  theory  generally  accepted,  an  anti- 
frictional  alloy  should  consist  of  hard  grains,  to  carry  the 
load,  which  are  imbedded  in  a  matrix  of  plastic  material,  to 
enable  it  to  mold  itself  to  the  journal  without  undue  heat- 
ing. Such  a  condition  would  be  met  in  a  lead  and  antimony 
alloy  having  above  13  per  cent  antimony,  but  it  is  not  advis- 
able to  use  more  than  25  per  cent  antimony,  as  the  composi- 
tion would  be  too  brittle.  The  Pennsylvania  Railroad  Co. 
has  adopted  the  13  per  cent  antimony-lead  alloy  as  a  filling 
metal  for  bearings,  in  order  to  obtain  the  best  results. 

The  friction  becomes  less  with  an  increase  of  antimony, 
and  the  temperature  of  running  is  likewise  diminished 
when  running  under  normal  conditions ;  but  the  harder  the 
alloy,  the  more  difficulty  is  experienced  in  bringing  it  pri- 
marily to  a  perfect  bearing,  and  the  greater  the  liability  of 
heating  through  aggravated  conditions.  The  wear  on  the 
journal  is  not  decreased  with  increasing  hardness,  as  might 
be  expected.  This  journal  wear  is  in  all  probability  not  due 
so  much  to  the  alloy  directly  as  it  is  to  the  fact  that  the  soft- 
er metals  collect  grit,  principally  from  the  small  particles 
of  steel  from  the  worn  journal,  and,  acting  as  a  lap,  cause 
rapid  wear.  With  the  harder  metals  these  particles  are 
worked  out  without  becoming  imbedded.  The  cost  of  the 
lead  and  antimony  alloy  is  very  low.  It  can  be  used  in 
many  services  where  higher-priced  alloys  are  relied  upon 
mainly  for  their  high  cost.  It  is  one  of  the  greatest  ex- 


34  BEARING   METALS 

travagances  of  large  industrial  establishments  to  use  mate- 
rials that  are  too  good  for  certain  uses,  and  even  perhaps 
unsuited,  under  the  supposition  that  they  must  be  good  be- 
cause they  are  expensive.  This  fact  has  no  greater  exempli- 
fication than  in  the  purchase  of  babbitt  metal,  and  is  due  to 
the  great  uncertainty  which  exists  not  only  among  users, 
but  among  the  manufacturers  of  these  bearing  metals. 

Alloys  of  Lead,  Antimony,  and  Tin.  It  should  not  be  as- 
sumed that  antimony-lead  is  the  cheapest  alloy  to  use  under 
all  circumstances,  because,  when  high  pressures  are  to  be 
encountered,  tin  is  a  very  desirable  adjunct.  Tin  imparts 
to  the  lead-antimony  alloy  rigidity  and  hardness  without 
increasing  brittleness,  and  can  produce  alloys  of  sufficient 
compressive  strength  for  nearly  all  uses.  The  structure  of 
a  triple  alloy  of  this  nature  is  quite  complicated,  and  not  yet 
sufficiently  defined.  The  cost  of  the  alloy  increases  with 
an  increase  of  tin;  but,  for  certain  uses,  where  sufficient 
compressive  strength  cannot  be  obtained  by  antimony,  be- 
cause of  its  accompanying  brittleness,  it  is  indispensable, 
and  will  answer  in  nearly  every  case  where  the  tin  basis 
babbitts  are  used. 

Alloys  of  Tin  and  Antimony.  These  alloys  are  seldom 
used  alone  as  bearing  metals,  but  are  extensively  used  for 
so-called  "Britannia  ware,"  and  in  equal  proportions  for 
valve  seats,  etc. 

Alloys  of  Tin,  Antimony  and  Copper.  This  combination 
is  what  is  known  as  genuine  babbitt,  after  its  inventor, 
who  presumably  was  the  first  man  to  conceive  the  idea  of 
lining  bearings  with  fusible  metal.  Alloys  of  this  compo- 
sition are  among  the  most  generally  used  bearing  metals. 
They  form  a  large  group  of  varying  compositions,  some  of 
which  are  given  in  the  following,  under  "Babbitt  Metal." 

Alloys  of  Tin,  Antimony,  Lead,  and  Copper.  Lead,  al- 
though a  soft  metal,  renders  this  alloy,  when  added  in  but 
small  proportions,  harder,  stiffer,  more  easily  melted,  and 
superior  in  every  way  to  the  alloy  without  it.  This  is  one 
of  the  instances  where  cheapening  of  the  product  is  bene- 
ficial. 


BEARING   METALS 


35 


The  foregoing  represents  the  more  important  combina- 
tions of  alloys  of  tin  and  lead  basis.  These  alloys  are  of 
far  more  importance  in  the  arts  than  the  white  metals,  the 
main  portion  or  basis  of  which  is  zinc.  At  various  times 
new  combinations  of  zinc  have  been  proposed,  but,  with 
very  few  exceptions,  they  have  not  come  into  common  use 
for  two  reasons:  First,  because  of  the  great  tendency  of 
zinc  to  adhere  to  iron  when  even  slightly  heated.  What  is 
technically  known  as  galvanizing  the  journal  is  caused  by 
these  conditions ;  second,  because  of  the  brittleness  produced 
under  the  effects  of  heat,  such  as  is  produced  by  friction 

Table  I.    Babbitt  Metal  Compositions 


Class  of  Service  Adapted  for 

Composition   of   Metal 

Tin 

Anti- 
mony 

Cop- 
per 

Lead 

High-pressure  bearings  

90 
86 
30 
15 
8 

7 
12 
20 
25 
20 
10 

3 
2 

50 
60 
72 
90 

High  pressure  and  fast  speed.  .  . 

Medium  pressure  and  high  speed  .  . 
Medium  pressure  and  medium  speed  . 
Low  pressure  and  medium  speed.  .  . 
Principally  for  shaftings,  etc  

when  lubrication  is  interfered  with,  and  consequent  danger 
of  breakage. 

Babbitt  Metal.  Babbitt  is  the  name  given  to  a  great  vari- 
ety of  white-metal  alloys  used  as  linings  for  bearings.  The 
name  is  derived  from  that  of  the  inventor,  Isaac  Babbitt, 
who,  in  1839,  obtained  a  patent  for  a  special  type  of  bear- 
ing enclosing  a  soft-metal  alloy.  This  bearing  had  lips  ex- 
tending around  the  ends  to  retain  the  soft  metal  in  case  of 
accidental  heating,  and  also  to  prevent  the  soft  metal  lining 
from  being  spread  out  when  subjected  to  heavy  pressure. 

Composition  of  Babbitt  Metal.  The  exact  composition 
of  the  original  babbitt  metal  is  not  known.  The  ingredients 
were  copper,  tin,  and  antimony,  in  approximately  the  fol- 
lowing proportions :  89.3  per  cent  of  tin ;  3.6  per  cent  of 
copper;  7.1  per  cent  of  antimony.  This  metal  possesses 
great  anti-frictional  qualities,  but  the  high  percentage  of 
tin  makes  it  expensive  and  has  led  to  the  substitution  of 


36 


BEARING   METALS 


other  metals  which  are  marketed  under  the  name  of  "babbitt 
metal."  These  cheaper  grades,  when  properly  made,  are 
superior  to  the  original  babbitt  metal  for  some  purposes. 
The  composition  of  babbitt  metal  should  be  varied  accord- 
ing to  the  pressure  to  which  it  will  be  subjected  and  the 
speed  of  the  rotating  member ;  the  size  of  the  bearing  and 
thickness  of  the  babbitt  metal  lining  should  also  be  consid- 
ered. While  it  is  not  necessary  to  use  a  different  composi- 
tion for  each  slight  variation,  a  different  grade  is  prefer- 
able when  the  conditions  are  radically  different.  The  com- 
positions of  metals  for  different  classes  of  bearings  fre- 
quently used  are  given  in  Table  I. 

Table  II.    Babbitt  Metal  Compositions 


Number 

Tin, 
Per  cent 

Antimony, 
Per  cent 

Copper, 
Per  cent 

Lead, 
Per  cent 

1 

83.33 

8.33 

8  33 

2 

89.00 

700 

4.00 

3 
4 

50.00 
5.00 

15.00 
15  00 

2.00 

33.00 
80.00 

5 

10  00 

90  00 

Babbitt  for  Sub-press  Slides.  One  of  the  uses  for  babbitt 
is  in  sub-presses  where  the  plunger  slides  up  and  down.  A 
special  babbitt  is  used  for  this  purpose  consisting  of  66  per 
cent  of  lead,  18  per  cent  of  antimony,  and  16  per  cent  of  tin. 

American  Society  for  Testing  Materials  Specifications  for 
Babbitt  Metals.  A  sub-committee  of  the  American  Soci- 
ety for  Testing  Materials  has  proposed  to  reduce  the  large 
number  of  babbitt  metals  in  use  to  five,  a  number  which  the 
committee  thinks  will  be  ample  for  every  class  of  work. 
Table  II  gives  the  composition  of  the  series  which  it  is  be- 
lieved covers  the  range  for  all  requirements. 

Where  cost  is  of  no  great  importance,  the  original  babbitt 
formula  is  still  considered  the  standard  of  excellence  in  the 
trade,  and  has  been  adopted  by  many  of  the  leading  rail- 
roads, the  United  States  Government,  and  many  industrial 
establishments.  It  is  used  in  the  majority  of  cases  where 
cheaper  composition  would  do  equally  as  well.  It  is  the 
most  costly  bearing  alloy,  due  to  the  high  content  of  tin. 


BEARING   METALS  37 

S.  A.  E.  Standard  Babbitt  Metal.  The  babbitt  metal 
adopted  as  a  standard  by  the  Society  of  Automotive  Engi- 
neers, Inc.,  is  a  special  grade  owing  to  the  large  amount  of 
copper  contained  therein.  It  is  used  for  the  connecting-rod 
linings  of  motor  bearings,  or  any  service  where  machinery 
designers  are  confronted  with  severe  operating  conditions. 
The  composition  follows : 

Tin   84.00  per  cent 

Antimony 9.00  per  cent 

Copper 7.00  per  cent 

A  variation  of  1  per  cent  either  way  will  be  permissible 
in  the  tin,  and  0.5  per  cent  either  way  will  be  permissible  in 
the  antimony  and  copper.  The  use  of  other  than  virgin 
metals  is  prohibited.  No  impurity  will  be  permitted  other 
than  lead,  and  that  not  in  excess  of  0.25  per  cent. 

Properties  of  Babbitt  Metal.  Babbitt  metal  and  the  white- 
metal  alloys,  generally,  not  only  have  valuable  "anti- 
frictional"  properties,  but  other  important  advantages. 
They  may  easily  be  melted  in  an  ordinary  iron  ladle,  so  that 
little  equipment  is  required  for  re-lining  a  bearing;  they 
are  durable  and  wear  remarkably  well ;  they  tend  to  reduce 
shocks  and  deaden  noise;  and  they  can  readily  be  provided 
with  grooves  for  lubrication  and  are  easily  fitted  to  obtain 
a  uniform  bearing.  These  alloys,  however,  are  liable  to  melt 
and  run  out  of  the  bearing  shell  in  case  of  accidental  over- 
heating. Overheating  of  other  bearing  materials  which 
would  not  melt  and  flow,  however,  would  cause  equally  dis- 
astrous results  as  to  their  bearing  properties.  The  follow- 
ing information  on  babbitt  bearing  metals  was  given  by 
T.  J.  Johnston  in  The  Electric  Journal. 

A  good  bearing  material  must  fulfill  the  following  re- 
quirements :  It  must  be  of  sufficient  strength  to  sustain  its 
load ;  it  must  not  heat  rapidly ;  it  must  be  easily  worked ;  it 
must  have  good  anti-frictional  properties;  it  must  have  a 
long  life  with  small  loss  of  material  due  to  wear ;  and  (with 
the  exception  of  cast  iron  on  cast  iron  and  hardened  steel  on 
hardened  steel)  it  will  usually  be  a  material  of  an  entirely 
different  molecular  construction  from  that  of  the  revolving 
journal  which  it  must  support.  The  journal,  when  running, 


38  BEARING   METALS 

may  be  completely  borne  by  the  oil  film  but,  during  the  time 
of  starting  or  stopping,  the  film  is  broken,  minute  irregular- 
ities on  the  surfaces  of  the  bearing  and  journal  engage, 
and,  if  the  bearing  does  not  yield,  as  in  the  case  of  a  steel 
bearing  and  a  steel  journal,  small  particles  are  fused  and 
torn  out;  these  accumulate  at  the  entrance  point,  and  may 
cut  both  the  bearing  and  the  journal.  With  a  steel  journal 
running  in  a  white-metal  bearing,  the  bearing  surface  is 
entirely  different  in  its  molecular  structure,  the  bearing  in- 
equalities are  not  strong  enough  to  resist  the  minute  inequal- 
ities in  the  journal,  and  so,  instead  of  fusing,  they  yield  and 
are  smoothed  out ;  consequently,  the  bearing  surface,  instead 
of  being  injured  by  contact  and  momentary  high  coefficient 
of  friction,  is  smoothed  and  burnished,  thus  preparing  the 
way  for  a  uniform  wedge  oil  film  with  a  minimum  coefficient 
of  running  friction. 

Laboratory  tests  show  that  a  lead-base  babbitt  will  give 
very  good  results,  but  such  tests  of  bearing  materials  are 
difficult  and  uncertain,  and  apt  to  be  misleading.  Similarly, 
chemical  tests  cannot  be  relied  upon  entirely,  since  a  great 
deal  is  dependent  on  the  actual  making  of  the  babbitt.  Lab- 
oratory and  chemical  tests,  taken  in  conjunction  with  actual 
service  tests,  furnish  reliable  data,  and  a  bearing  metal  de- 
veloped along  these  lines  may  be  counted  upon  to  give  con- 
sistent results  in  practical  work.  Babbitts  made  up  accord- 
ing to  nearly  300  different  formulas  are  at  present  on  the 
market.  It  would  be  of  very  great  benefit  to  the  users  of 
babbitt  if  this  number  were  greatly  reduced  and  the  process 
of  manufacture  so  standardized  as  to  insure  a  uniform  qual- 
ity of  alloy.  Except  for  a  few  cases,  but  two  babbitts,  one 
a  lead-base  alloy,  the  other  a  tin-base  alloy,  each  being  the 
best  that  can  be  made,  are  required  for  a  complete  line  of 
bearings,  ranging  in  weight  from  a  few  ounces  to  several 
tons. 

Bronze  Bearing  Metals.  Bronze  is  the  term  which  origi- 
nally was  applied  to  alloys  of  copper  and  tin  as  distinguished 
from  alloys  of  copper  and  zinc.  A  bronze  is  usually  under- 
stood to  have  more  copper  than  tin,  and  the  properties  of 
the  metal  differ  widely  according  to  the  percentages  of  these 


BEARING   METALS  39 

f 

constituents  which  are  present.  In  general,  the  alloy  hard- 
ens when  tin  is  present  up  to  proportions  of  30  per  cent  or 
a  little  over,  and,  when  this  limit  is  exceeded,  it  takes  on 
more  and  more  the  nature  of  tin  until  pure  tin  is  reached. 
From  a  scientific  point  of  view,  this  alloy  is  one  of  the  most 
interesting,  and  has  attracted  the  attention  of  many  investi- 
gators, who  have  spent  years  of  study  on  it,  to  learn  its 
various  properties  and  explain  its  constifution. 

The  alloys  of  interest  in  this  connection,  however,  are 
those  which  are  so  constituted  as  to  be  adapted  for  bearing 
purposes.  These  would  be  said  to  contain  from  3  to  15  per 
cent  of  tin,  and  from  85  to  97  per  cent  of  copper.  The  alloy 
of  tin  containing  a  small  percentage  of  copper  is  often  used 
as  a  babbitt  metal,  but  this  comes  under  the  class  of  white 
metals,  which  have  already  been  discussed.  Bronze  contain- 
ing above  15  per  cent  of  tin  has  been  recommended  at  vari- 
ous times  for  bearings,  owing  to  its  hardness,  but  such  a 
bearing  demands  mechanical  perfection  and  perfect  lubrica- 
tion. It  has  no  plasticity  of  its  own,  and,  as  soon  as  the  oil 
film  is  interrupted,  rapid  abrasion  and  "seizure"  take  place, 
with  hot  boxes  as  the  result.  The  very  erroneous  idea  is  still 
held  by  many  that,  to  resist  wear  and  run  with  the  least  pos- 
sible friction,  a  bearing  alloy  must  be  as  hard  as  possible. 
It  is  true  that  hard  bodies  in  contact  move  with  less  friction 
than  soft  ones,  but  the  alloy  which  is  the  least  liable  to  heat 
and  cause  trouble  is  the  one  which  will  stand  the  greatest 
amount  of  abuse ;  that  is,  an  alloy  which  has  sufficient  plas- 
ticity to  adapt  itself  to  the  irregularities  of  service  without 
undue  wear.  The  alloys  of  copper  and  tin  were  used  exten- 
sively some  twenty  or  twenty-five  years  ago,  and  were  con- 
sidered the  standard  for  railroad  and  machinery  bearings. 
The  old  alloy,  known  as  "cannon  bronze,"  containing  7  parts 
of  copper  and  1  part  of  tin,  is  still  specified  by  a  few  unpro- 
gressive  railroad  men  and  machinery  builders. 

Bronze  Containing  Copper,  Tin,  and  Lead.  This  compo- 
sition is  now  the  recognized  standard  bearing  bronze,  its  ad- 
vantage over  the  bi-compound  coming  from  the  introduction 
of  lead.  The  bronze  containing  lead  is  less  liable  to  heat 


40  BEARING   METALS 

x 

under  the  same  state  of  lubrication,  etc.,  and  the  rate  of 
wear  is  much  diminished.  As  lead  is  cheaper  than  tin,  it  is 
desirable  to  produce  a  bearing  metal  with  as  much  lead  and 
as  little  tin  as  possible.  The  metal  known  as  "Ex.  B."  com- 
position (tin,  7  per  cent;  lead,  15  per  cent;  copper,  78  per 
cent)  is  stated  to  be  the  best  that  can  be  devised.  This  alloy 
contains  the  smallest  quantity  of  tin  that  will  hold  the  lead 
alloyed  with  the  copper.  By  adding  a  small  percentage  of 
nickel,  however,  to  the  extent  of  from  1/2  to  1  per  cent,  a 
larger  proportion  of  lead  may  be  used,  and  successful 
bronzes  have  been  made  by  this  process,  which  contained  as 
much  as  30  per  cent  of  lead.  Such  bronzes,  containing  a 
large  amount  of  lead,  through  the  addition  of  nickel,  are 
known  in  the  trade  as  "Plastic  bronzes"-  and  are  a  regular 
commercial  article. 

Undoubtedly,  in  investigations  in  this  field,  sufficient  at- 
tention has  not  been  paid  to  the  effect  of  temperature  on  the 
bearing  properties  of  the  alloys  used  for  these  bearings. 
More  rigid  investigation  in  this  field  and  limitations  in  re- 
gard to  the  temperatures  permissible,  with  means  for  main- 
taining these  within  fairly  close  limits,  will  undoubtedly  re- 
sult in  a  great  increase  in  the  possibility  of  improvements  in 
speed  and  weight  of  various  types  of  machinery.  More  or 
less  extensive  experiments  along  these  lines  are  being  con- 
ducted in  regard  to  the  bearings  used  in  turbine  construc- 
tion, since  the  speed  here  has  rendered  the  problem  an  acute 
one  and  is  necessary  for  efficient  operation  of  the  turbine 
itself. 

Commercial  Bearing  Metals.  Table  III,  "Composition  of 
Alloys  Used  for  Bearing  Metals,"  shows  the  various  con- 
stituents of  the  more  or  less  common  bearing  metals  now 
on  the  market.  A  wide  deviation  in  the  composition  of  bab- 
bitt is  shown  in  the  first  part  of  the  table.  The  first  babbitt 
is  a  fairly  good  alloy  for  high-speed  machinery,  but  is  not 
very  hard.  Its  melting  point  is  about  500  degrees  F. ;  in 
fact,  the  properties  of  all  alloys  or  bearing  metals  can  be 
very  widely  deduced  from  their  melting  point.  The  second 
babbitt  is  somewhat  harder  and  melts  at  a  higher  point. 
Both  of  these  are  used  largely  for  lining  purposes.  The 


BEARING   METALS 


41 


fourth  babbitt  is  used  very  widely  for  heavy  machinery. 
All  of  the  babbitts  mentioned  have  been  fairly  successful. 
Babbitt  6  has  good  wearing  properties,  but  cannot  be  used 
for  high  speeds.  Most  of  the  other  metals  included  in  the 
table,  where  copper  is  not  used  in  excess,  can  be  regarded 
as  in  the  same  class  as  babbitts.  The  "white"  class  has  a 
fairly  good  electrical  conductivity,  much  greater  than  that 
of  ordinary  babbitt,  and  is  used  in  the  bearings  of  gener- 
ators, motors,  electric  cars,  etc.  In  alloys  containing  sodium 

Table  III.    Composition  of  Alloys  Used  for  Bearing  Metals 


Alloys 

Lead 

Tin 

Anti- 
mony 

Cop- 
per 

Zinc 

Other 

Constit- 
uents 

Babbitt   1 

80.0 

20.0 

Babbitt   2 

72.0 

21.0 

7.0 

Babbitt   3  

70.0 

10.0 

20.0 

Babbitt   4  

80.5 

11.5 

7.5 

0.5 

Babbitt    5 

0.5 

68.0 

1  0 

30  5 

Babbitt    6 

20.0 

80  0 

Babbitt   7 

86.0 

10  0 

4  o 



White  metal   1  

82  .  0 

12.0 

6  0 

White  metal   2  .... 

3.0 

7.6 

3.8 

2  3 

83  3 

White  brass  

64.0 

2  0 

34  0 

Bronze    1 

11  5 

11  5 

77   0 

Bronze    2 

15  0 

8  0 

76   2 

•   •   *   * 

p  —  A   on 

Bronze    3 

9  5 

10  0 

8ft   ^ 

*   .    •   . 

Bronze    4 

3  0 

07   o 

•    •   •   • 



Bronze1    5 

15  0 

CK   A 

•   •   •   * 

****** 

Bronze    6 

15  0 

7  0 

78   0 

.... 

****** 

Note:  P   indicates  phosphorus. 

the  oxidation  of  the  sodium  produces  a  material  which  will 
saponify  with  the  oil  used  in  the  bearing  and  produce  soap, 
thus  assisting  lubrication.  Practically  no  experiments 
have  been  made  to  determine  the  extent  and  amount  of  such 
action.  Possibilities  along  this  line,  however,  are  great,  not 
only  for  this  particular  alloy,  but  for  many  others  not  as  yet 
considered. 

The  other  alloys  included  in  the  table  consist,  to  a  very 
great  extent,  of  copper,  tin,  and  lead,  and  usually  have  a 
thin  liner  of  lead  or  some  soffbabbitt,  and  hence  wear  much 
better  than  an  entire  bearing  of  the  soft  babbitt.  The  ten- 
dency to  wear  decreases  with  increase  of  lead  and  increase 


42 


BEARING   METALS 


of  tin.  Increase  of  lead,  of  course,  affects  the  frictional 
quantities  of  the  alloy,  hence  its  heating  properties.  A  cer- 
tain amount  of  other  metal,  however,  is  necessary  to  keep 
the  lead  from  separating  from  the  copper.  The  "P.  R.  R. 
car  brass,  B"  is  considered  one  of  the  best  bearing  bronzes 
that  can  be  obtained.  It  contains  approximately  the  small- 
est quantity  of  tin  that  will  hold  the  lead  alloyed  with  the 
copper.  Table  IV,  "Composition  of  Bronzes/'  gives  a  list  of 
alloys  used  by  the  U.  S.  Navy  Department. 

Table  IV.   Composition  of  Bronzes 


Alloys 

Lead 

Tin 

Anti- 
mony 

Cop- 
per 

Zinc 

White  metal  
Hard  bronze  for  pis- 
ton rings  

3.0 

7.6 
22.0 

30 
.  5 

2.3 

78  0 

83.3 

Bearings   -  -   w  e  a  r- 
ing  surfaces,  etc.. 
Naval   brass  
Brazing  metal  



13.5 
1.0 

83.0 
62.0 
85.0 

3.5 
37.0 
15.0 

Substitutes  for  Tin  in  Bearing  Metals.  The  Bureau  of 
Standards,  in  its  efforts  to  determine  to  what  extent  substi- 
tutes may  be  used  for  tin,  calls  attention  to  the  limited  sup- 
ply and  great  demand  for  this  metal,  and  mentions  that  it  is 
imperative  that  steps  be  taken  at  once  to  eliminate  all  waste 
of  tin  and  to  use  substitutes  or  reduce  its  use  as  far  as  pos- 
sible and  practicable  in  all  alloys.  It  is  pointed  out  that 
many  specifications  for  bearing  metals  now  in  existence  call 
for  pure  tin,  and  that  a  large  saving  of  high  grades  of  tin, 
such  as  Banca  or  Straits,  could  be  brought  about  by  allow- 
ing the  use  of  second  quality  pig  tin  in  making  tin-base 
babbitt.  Detrimental  impurities  could  still  be  limited,  but  a 
maximum  of  1  per  cent  of  lead  could  be  allowed.  This  would 
not  be  harmful  to  a  tin-base  or  lead-base  lining  metal.  There 
is  no  question  but  that  the  tin  content  could  be  reduced 
somewhat  in  all  bearing  alloys.  Every  possible  saving 
should  be  effected.  For  those  cases  where  genuine  babbitt 
is  now  used  and  which  require  a  very  high  grade  of  lining, 
alloys  are  suggested  containing  either  of  the  combinations, 


BEARING   METALS  43 

85  per  cent  tin,  10  per  cent  antimony,  and  5  per  cent  copper ; 
or  65  per  cent  tin,  from  3  to  6  per  cent  copper,  and  from  28 
to  30  per  cent  zinc. 

Lead-base  linings  can  be  satisfactorily  used  in  many  cases 
where  tin-base  linings  are  now  in  use,  and  in  fact  the  change 
has  already  been  made  in  some  shops,  although  the  substitu- 
tion should  be  more  general.  Several  special  types  of  lead- 
base  linings,  hardened  with  alkali  earth,  are  reported  to  be 
giving  very  satisfactory  service  in  the  place  of  high  tin  bab- 
bitt. Two  other  alloys  containing  large  percentages  of  lead 
and  zinc  have  apparently  been  found  to  perform  the  same 
services  which  were  required  of  tin-base  linings  in  machine 
tool  work.  One  of  these  alloys  consists  of  8  per  cent  tin,  8 
per  cent  antimony,  4  per  cent  copper,  and  80  per  cent  lead ; 
and  the  other  conists  of  5  per  cent  tin,  7  per  cent  antimony, 
2  per  cent  copper,  10  per  cent  lead,  and  76  per  cent  zinc. 

One  way  in  which  a  lining  metal  can  be  saved  is  to  use 
as  thin  a  lining  as  is  possible  in  order  to  maintain  a  high 
enough  temperature  during  pouring  to  guarantee  a  firm 
bond  and  solid  mass  of  metal.  In  place  of  a  bronze  bearing 
containing  80  per  cent  copper,  10  per  cent  tin,  and  10  per 
cent  lead,  an  addition  of  a  small  percentage  of  zinc  or  phos- 
phor-copper and  an  increase  of  the  lead  content  will  result 
in  a  saving  of  at  least  25  per  cent  of  the  tin  ingredient. 

Comparison  of  Lead-base  and  Tin-base  Babbitt  Metals. 
Tenacity  is  desirable  in' a  bearing  metal,  especially  at  the 
higher  bearing  temperatures,  as  bearings  fail  because  of 
warping  or  deformation.  The  following  information  on  the 
relative  merits  of  lead-base  and  tin-base  babbitt  metals  was 
abstracted  from  a  paper  presented  before  the  American  In- 
stitute of  Mining  Engineers  by  J.  L.  Jones,  metallurgist, 
Westinghouse  Electric  &  Mfg.  Co. 

The  Brinell  test  is  commonly  regarded  as  a  measure  of 
tenacity ;  in,  fact,  the  proposition  has  been  made  to  substi- 
tute for  the  term  "Brinell  hardness  number"  the  expression 
"tenacity  number."  Brinell  tests  at  progressively  increasing 
temperatures  showed  that  the  lead-base  babbitt  has  a  better 
resistance  to  deformation  at  the  working  temperatures  than 
babbitts  with  a  tin  base.  The  tests  were  made  on  disks  4 


44  BEARING   METALS 


inches  in  diameter  and  l1/^  inches  thick  of  the  following 
composition  : 

Antimony,     Copper,          Lead,  Tin, 

Babbitt  Per  cent       Per  Cent    Per  Cent  Per  Cent 

A 8  2  0          90 

B 81/3         81/3         0          83 1/3 

C 14  0  78  8 

The  disks  were  heated  by  an  electric  hot  plate,  the  tem- 
perature being  controlled  by  suitable  rheostats.  Pyrometer 
leads  were  soldered  in  the  center  of  each  disk.  The  disks 
were  well  insulated  to  prevent  radiation  loss  and  were  held 
at  the  desired  temperature  for  several  minutes  to  guard 
against  variation.  The  tests  were  made  on  the  bottom  sur- 
face of  the  disks  after  a  light  machine  cut  was  taken  to 
secure  a  perfectly  planed  surface.  The  Brinell  hardness 
numbers  obtained  at  the  various  temperatures  were  plotted 
and  the  results  are  shown  by  the  curves  given  in  Fig.  1.  At 
35  degrees  C.  the  hardness  of  the  babbitts  A  and  C  is  identi- 
cal, but  above  this  temperature  the  lead-base  babbitt  has  the 
higher  hardness  number.  The  curves  of  babbitts  B  and  C 
are  almost  parallel  and  not  very  far  apart.  Complete  re- 
sults from  various  test  floors,  covering  a  number  of  gears 
and  a  variety  of  motors,  confirm  the  superiority  of  the  lead- 
base  babbitt.  In  one  case  where  it  was  necessary  to  reline 
one  hundred  bearings  containing  babbitt  A  in  a  month,  it 
was  necessary  to  reline  only  about  six  bearings  that  con- 
tained the  lead-base  babbitt  C.  As  a  result,  the  lead-base 
babbitt  was  substituted  for  all  classes  of  machines  and  the 
tin-base  babbitt  A  eliminated  altogether. 

While  the  Brinell  hardness  shown  in  the  chart  for  the 
babbitts  A  and  C  is  not  far  from  the  average  hardness  found 
for  these  alloys  when  using  the  standard  hardness  test  piece, 
the  results  obtained  for  the  hard  babbitt  B  is  much  below 
the  normal.  This  probably  is  due  to  the  difficulty  of  pre- 
venting the  large  amount  of  copper  in  this  babbitt  from 
segregating  even  when  kept  very  hot  and  being  stirred  con- 
tinuously. The  copper  falls  to  the  bottom  of  the  melting 
pot;  hence  when  stirring,  the  aim  should  be  to  bring  the 
metal  from  the  bottom  of  the  pot  to  the  top. 


BEARING   METALS 


45 


Effect  of  Lead  on  Babbitt.  It  is  a  common  belief  that  the 
addition  of  even  a  small  amount  of  lead  to  a  genuine  bab- 
bitt renders  it  inferior.  Fig.  2  shows  the  results  of  tests 
made  with  the  tin-base  babbitt  A  to  which  has  been  added 
1,  3,  and  5  per  cent  of  lead,  the  results  being  shown  by  curves 
B,  C,  and  D,  respectively.  These  results  show  that  when  a 


80 
70 
60 

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o 
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40 
30 
20 

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/ 

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/ 

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/ 

/ 

/ 

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B/ 

/ 

9 

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f 

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/ 

/ 

/ 

/ 

/ 

/ 

/ 

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OFC 

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^H^oo^usos^ooeoooeoooeooo-sioiiii-it-eoo 

gj  £  S3  £J  £  3  8  SJ  cS  §3  §3  8  S3  d  53  8*  8  8  3  S  2 

BRINELL  HARDNESS  NUMBER 

^COC<IC>ioOJCT>mCVJO 
3    O0a6tr~t^t^e0t0t0\f 

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Fig.    1.      Hardness    of    Representative    Babbitts    at    Varying 
Temperatures 

small  amount  of  lead  is  accidentally  added  to  the  tin-base 
babbitt  its  hardness  and  anti-frictional  qualities  are  much 
improved.' 

Effect  of  Compression  on  Brinell  Hardness  of  Babbitt. 
In  the  case  of  large  bearings,  peening  or  compressing  the 
babbitt  by  means  of  hammering  is  often  specified,  it  being 
supposed  that  by  just  compressing  or  densifying  the  babbitt 


46 


BEARING   METALS 


and  hardening  it  the  bearing  will  give  better  service.  In 
one  case  where  two  phosphor-bronze  plates  were  coated  with 
babbitts  B  and  C,  then  subjected  to  pressures  varying  from 
8500  to  13,000  pounds  per  square  inch,  it  was  found  that  the 
lead-base  babbitt  stood  up  better  than  the  tin-base  babbitt. 
When  the  load  was  increased  to  30,000  pounds  per  square 


50 


%/ 


5  ^ILLIMETER 
PRESS'ION 


3  §3'  S3  S  8  8 


BRINELL  HARDNESS  NUMBER 


Machinery 


Fig.  2.     Effect  of  Lead  on   Hardness  of  a  Babbitt 

inch,  the  tin-base  babbitt  presented  a  better  appearance,  as 
it  flowed  uniformly  over  the  edge  of  the  bronze  square  in  all 
directions,  while  the  lead-base  babbitt  was  compressed  more 
on  one  side  than  on  the  other.  The  tests  show  that  broach- 
ing, peening,  etc.,  do  not  appreciably  increase  the  hardness 
of  babbitt ;  hardness  must  be  obtained  through  quickly  cool- 
ing the  babbitt  lining  by  means  of  water-cooled  mandrels, 
etc.  A  microscopic  examination  of  a  lead-base  babbitt 


BEARING   METALS  47 

shows  that  the  metals  tend  to  segregate.  This  lack  of  uni- 
formity may  be  guarded  against  by  pouring  a  thin  lining 
and  chilling  quickly.  The  secret  of  obtaining  good  bearings 
consists  in  keeping  the  matrix  tough  and  hard.  There  is  less 
tendency  for  tin  antimonide  crystals  in  tin-base  babbitts  to 
rise  to  the  surface,  because  of  the  lower  gravity  of  these 
babbitts. 

Miscellaneous  Bearing  Metals.  A  high-class  bearing 
metal  is  prepared  as  follows :  Melt  7  parts  of  copper  at  as 
low  a  heat  as  possible;  then  add  25  parts  of  antimony  and 
200  parts  of  tin.  This  mixture  is  cast  in  iron  ingot  molds. 
It  is  then  remelted  and  to  each  five  pounds  of  the  ingots  is 
added  eight  pounds  of  tin,  this  second  alloy  being  cast  in 
bars  to  suit  the  requirements. 

For  an  anti-friction  metal  that  can  be  subjected  to  pres- 
sures up  to  about  400  pounds  per  square  inch,  the  following 
composition  has  been  recommended :  Lead,  85  per  cent ; 
antimony,  10  per  cent;  and  tin,  5  per  cent.  For  pressures 
exceeding  400  pounds  per  square  inch,  the  following  alloy 
will  prove  satisfactory:  Tin,  85  per  cent;  copper,  5  per 
cent;  and  antimony,  10  per  cent.  This  alloy  can  be  used 
safely  for  pressures  up  to  1000  pounds  per  square  inch.  The 
alloys  in  Table  V  are  stated  to  have  given  complete  satis- 
faction for  the  purposes  mentioned. 

An  alloy  made  by  melting  together  approximately  equal 
parts  of  cadmium  and  zinc,  with  an  addition  of  a  small  pro- 
portion of  antimony  is  said  to  be  superior  to  the  usual  white 
metal.  It  is  very  easily  worked  and  particularly  easily 
turned,  it  fills  up  the  mold  completely  when  cast,  possesses 
relatively  great  hardness,  and,  what  is  most  important,  it 
has  an  extremely  small  coefficient  of  friction.  The  alloy  can 
consist  of  from  45  to  50  parts  of  cadmium;  from  45  to  50 
parts  of  zinc;  and  up  to  10  parts  of  antimony.  The  anti- 
mony added  should  not  exceed  10  per  cent,  as  otherwise  the 
metal  is  too  brittle.  A  very  suitable  proportion  of  antimony 
is  5  per  cent.  If  the  proportion  of  cadmium  and  zinc  is  con- 
siderably varied,  the  coefficient  of  friction  increases,  and 
the  other  good  properties  of  the  alloy  are  essentially  preju- 
diced. 


48 


BEARING   METALS 


Tests  on  Bearing  Metals.  The  R.  K.  LeBlond  Machine 
Tool  Co.,  Cincinnati,  Ohio,  has  made  a  comparative  test  of 
bearings  for  lathe  spindles  on  two  of  the  engine  lathes  in  its 
plant,  to  determine  the  relative  durability  of  the  following 
combinations,  viz.:  hardened  steel  journal  in  cast-iron  box; 
hardened  steel  journal  in  bronze;  soft  steel  journal  in 
bronze;  and  soft  steel  journal  in  babbitt.  The  experiment 
was  made  on  both  ends  of  the  spindles,  thus  making  the  four 
combinations  named.  Both  lathes  were  kept  in  constant 
use,  the  general  character  of  work  being  the  same  for  both. 
When  examined,  the  condition  of  the  hardened  steel  journal 
and  cast-iron  box  was  the  best  of  all,  neither  the  spindle  nor 

Table  V.    Miscellaneous  Bearing-  Metals 


Used  for 

Tin 

Lead 

Zinc 

Anti- 
mony 

Cop- 
per 

Bis- 
muth 

Dynamos  —  high-speed  

88 

8 

3  5 

ft     EC 

Marine  engines  .  .  . 

77 

17 

3 

q 

Eccentrics  

5 

77  75 

15 

0 

Oor 

Submerged  bearihgs  

40 

48 

10 

2 

Main  bearings 

34 

44- 

16 

Q 

Slides,  thrust  bearings  
Railway    trucks  

65 
42 

30 
56 

2.5 

2.5 
2 

... 

Axle-boxes  

74  55 

13  50 

1  80 

6.55 

3  6 

Plastic   metal  

80 

10 

1 

g 

1 

Genuine   babbitt    (hard)  .... 

80 

10 

10 

Genuine  babbitt    (No.  2)  
Universal  bearing  metal  

83 
6 

77.75 

9 

16 

8 

0.25 

the  box  being  appreciably  worn,  the  grinder  and  scraper 
markings  still  being  visible.  The  hardened  steel  journal  and 
bronze  box  combination  was  in  good  shape,  but  the  journal 
was  slightly  ridged  in  the  center,  showing  more  wear  than 
the  first.  The  soft  spindle  in  bronze  was  worn  appreciably, 
but  the  soft  spindle  in  babbitt  was  in  first-class  condition. 
The  front  bearings  were  provided  with  oil  rings  and  oil 
reservoirs,  and  the  main  bearings  with  oil  reservoirs  and 
felt  wicks. 

Investigations  to  ascertain  to  what  extent  repeated  melt- 
ings of  bearing  metals  influence  their  strength  and  reliability 
showed  the  following  results:    As   regards   white  metal 
(alloys  of  copper,  antimony,  and  tin)  it  was  found  that  re- 


BEARING   METALS  49 

peated  meltings  did  not  noticeably  alter  the  grain,  but  that 
the  rate  of  cooling  had  a  considerable  influence.  Quick  cool- 
ing yielded  a  finer  grain  and  a  higher  hardness  and  strength, 
and  it  is  recommended  that  white  metals  should  not  be  heat- 
ed to  high  temperatures  and  that  they  should  be  cooled  rap- 
idly. Bronze,  poor  in  tin,  and,  therefore,  comparatively 
inexpensive,  may  have  the  hardness  and  strength  increased 
by  being  rapidly  cooled  from  a  temperature  of  1440  de- 
grees F. 

While  a  great  deal  of  attention  has  been  given  to  the 
investigation  of  the  properties  of  bearing  metals,  there  is 
still  a  great  deal  to  be  done,  and  many  important  points  are 
yet  to  be  determined.  Apparently  many  bearing  metals  are 
unnecessarily  expensive,  containing  higher  percentages  of 
high-priced  metals  than  is  required. 


CHAPTER  III 
METHODS   OF   LUBRICATING    BEARINGS 

ASIDE  from  the  selection  of  the  lubricating  oil,  the  proper 
lubrication  of  bearings  requires  a  careful  study  of  the  best 
means  of  conducting  the  oil  to  the  bearing  surfaces  and 
also  means  of  protecting  the  bearing  against  the  entrance 
of  foreign  material  such  as  would  injure  the  surface.  Far 
more  attention  is  now  paid  to  these  details  than  was  the 
case  formerly,  especially  in  metal  working  machinery.  The 
higher  speeds  and  duties  which  prevail,  the  use  of  geared 
drives,  and  the  practice  of  boxing-in  portions  of  mechanism, 
have  all  had  their  effect  upon  the  methods  of  lubrication, 
and  many  new  and  improved  devices  have  been  developed 
and  come  into  general  use.  The  tendency  is  always  to  ren- 
der the  lubrication,  as  far  as  possible,  automatic  in  the  most 
complete  systems,  so  as  to  obviate  frequent  attention  on  the 
part  of  the  attendant,  and  to  minimize  the  consequences  of 
neglect.  The  details  of  construction  of  machine  tools  are  so 
complex  and  varied  that  it  is  not  surprising  to  find  a  multi- 
tude of  ways  of  supplying  oil  to  the  different  elements,  and 
the  principal  of  these  will  be  described  in  detail,  with  the 
help  of  typical  illustrations.  The  question  of  lubrication 
divides  itself  naturally  into  two  main  heads,  viz.,  supply  and 
distribution.  Subsidiary  to  these  are,  the  prevention  of  loss 
before  the  oil  has  done  its  work,  the  prevention  of  access  of 
dirt  to  the  surfaces,  and  the  final  catching  of  the  lubricant 
after  it  has  left  the  surfaces,  with  or  without  immediate  re- 
turn. In  many  instances,  it  is  necessary  to  prevent  escape 
of  oil  to  belts  and  surfaces  where  its  presence  is  undesirable. 

Oil  Supply.  The  oil  supply  is  effected  by  gravity,  by  pres- 
sure, by  capillary  attraction,  by  a  mechanical  lifting  action 
which  raises  oil  from  a  well,  or  by  contact,  through  the 

50 


LUBRICATING  BEARINGS  51 

medium  of  wicks,  pads,  or  rollers.  The  distribution  is  ef- 
fected by  rows  of  holes,  or  grooves,  by  wicks  or  pads  laid 
suitably,  by  rollers,  or  by  the  splash  method.  Such  varied 
conditions  are  met  with  that  it  is  impossible  to  claim  any 
particular  mode  -of  lubrication  as  being  the  best  for  shafts 
or  slides.  The  speed  of  rotation  may  make  a  vital  differ- 
ence in  the  results,  and  a  method  of  oiling  that  is  quite  sat- 
isfactory in  one  machine  may  be  undesirable  or  imprac- 
ticable in  another,  on  account  of  inaccessibility  of  the  parts 
or  great  increase  of  pressures.  With  the  use  of  the  boxed- 
in  geared  drives  in  so  many  types  of  metal  working  ma- 
chines, the  difficulties  of  reaching  the  parts  have  increased, 
and  some  rather  elaborate  devices  have  been  evolved  for 
supplying  and  catching  the  oil  without  having  recourse  to 
the  removal  of  covers.  Pipes  naturally  play  an  important 
part  in  the  conduction,  and  there  is  often  extensive  drilling 
of  shafts  and  bearings  for  the  purpose  of  conveyance  from 
the  outside. 

Quantity  of  Oil.  One  of  the  greatest  differences  which 
affect  the  lubricating  problem  is  the  quantity  of  oil  which 
has  to  be  supplied,  and  this  depends  on  the  function  of  the 
moving  part.  If  it  runs  at  a  good  speed,  under  consider- 
able duty,  a  copious  supply  is  essential  to  prevent  cutting 
and  heating,  but  if  the  movement  is  slow  or  intermittent 
and  the  work  light,  a  simpler  system  meets  the  case.  In 
sliding  ways,  which  run  at  high  speeds  and  carry  much 
weight,  ample  lubrication  is  imperative,  while,  on  the  other 
hand,  such  parts  as  cross-slides,  tool-boxes,  etc.,  which 
move  slowly  or  intermittently  will  retain  their  film  of  oil 
for  a  long  period  without  a  new  supply.  The  horizontal  or 
vertical  dispositions  of  sliding  surfaces  also  make  some  dif- 
ference in  the  amount  of  oil  which  can  be  fed.  Certain 
horizontal  ways  admit  of  flooding  without  inconvenience, 
while  this-  cannot  be  done  with  a  vertical  slide,  nor  would 
it  usually  be  necessary.  Even  when  ample  lubricant  is  fed 
to  a  bearing  or  slide,  this  is  of  little  avail  unless  distributed 
correctly  and  evenly,  so  that  no  parts  of  the  surfaces  be- 
come dry. 


52  LUBRICATING  BEARINGS 

It  is  not  sufficient  to  drill  a  hole  and  trust  that  the  oil 
will  get  between  two  surfaces  beyond  the  vicinity  of  the 
hole,  although  this  is  often  done  in  cheap  work.  The  oil 
must  be  distributed  to  the  right  and  left  in  a  definite  man- 
ner, with  due  allowance  for  possible  clogging.  The  two 
chief  methods  of  effecting  the  spreading  are  grooves  or 
channels,  and  pads  of  felt.  The  first  named  is  satisfactory 
provided  the  quantity  fed  in  is  sufficient  to  carry  it  the  re- 
quired distance;  the  latter  has  the  merit  of  absorbing  a 
good  deal  of  oil  and  keeping  the  surfaces  moist  for  a  cer- 
tain period,  even  if  neglected,  and  it  also  prevents  the 
access  of  grit  if  properly  fitted,  which  grooves  alone  do  not. 
Sometimes  a  compromise  is  made,  using  grooves  and  pads 
together.  If  the  pads  are  let  into  a  well  of  oil,  a  certainty 
of  supply  is  guaranteed,  although  this  will  not  distribute 
such  an  amount  of  oil  as  some  other  methods. 

The  arrangements  for  catching  and  draining  the  oil  from 
a  surface  or  bearing  influence  the  mode  of  feeding  to  a 
certain  extent,  and  the  two  must  be  intimately  related.  A 
copious  quantity  of  oil  does  not  do  much  good  if  it  is  per- 
mitted to  run  out  quickly  and  has  to  be  collected  in  a  primi- 
tive fashion,  with  inevitable  waste.  Under  the  pump  and 
flooded  bearing  system,  this  is  practicable,  but,  for  ordi- 
nary use,  a  moderate  amount  supplied  at  intervals  is  bet- 
ter. When,  however,  each  bearing  is  self-contained,  with  a 
ring-oiling  or  similar  system,  the  amount  of  oil  passing 
constantly  is  not  restricted,  but  depends  upon  the  method 
of  lifting  adopted.  There  is  no  waste  here,  because  the  oil 
from  the  surfaces  returns  to  the  reservoir  and  is  carried 
again  to  the  points  at  which  it  is  needed. 

Oil  Distribution.  In  the  means  provided  for  distributing 
and  catching  the  oil,  widely  varied  methods  are  adopted, 
ranging  from  simple  pots  or  troughs  under  open-ended 
bearings,  to  the  highly-elaborated  systems  in  which  a  forced 
supply  is  fed  to  the  bearings,  and  is  completely  collected 
from  these  and  returned  to  the  pump  for  use  over  again. 
The  latter  system,  if  properly  embodied  in  the  design  of  a 
machine,  is  the  best  solution  of  the  lubricating  problem, 


LUBRICATING  BEARINGS  53 

since  the  supply  is  constant  and  ample,  and  the  trouble  of 
attending  to  numerous  lubricators  is  obviated.  More  thor- 
ough flushing  of  the  bearings  is  also  insured,  and  any  dirt 
is  carried  away  quickly,  instead  of  being  churned  up  for  a 
considerable  period,  to  the  detriment  of  the  surfaces,  while 
the  cooling  is  also  more  effectual.  With  the  same  idea  in 
view  it  is  often  the  practice  to  obtain  the  oil  for  the  journal 
bearings  of  a  gear-box  from  the  well  in  which  the  gears 
splash  around,  in  place  of  providing  each  bearing  with  a 
separate  well. 

Methods  of  Supplying  Lubricants.  The  methods  of  feed- 
ing lubricants  vary  with  the  circumstances.  The  most  im- 
portant are : 

1.  The  simple  oil-hole,  fed  from  a  can,  with  no  means  of 
retaining  a  supply. 

2.  The  oil-cup  with  forced  feed,  obtained  by  screwing 
down  a  cap  or  plunger. 

3.  The  siphon  cup  with  a  wick  feeding  continually  by 
capillary  attraction. 

4.  The  grease-cup  device  with  constant  feed  by  spring 
pressure. 

5.  The  distributing  box  system  with  pipes  and  control 
taps  to  admit  certain  quantities  of  oil  to  the  leading-out 
pipes. 

6.  The  needle  lubricator  in  which  the  feed  is  produced 
by  the  vibration  caused  by  the  rotation  of  the  shaft. 

7.  The  oil-well  or  reservoir  which  is  filled  to  a  definite 
depth,  and  serves  to  lubricate  by  wicks,  etc.,  or  by  the 
splash  method  for  a  long  period. 

8.  The  force-pump  which  delivers  a  large  amount  of  oil 
to  one  or  several  locations. 

It  is  necessary  to  provide  some  way  of  observing  the  sup- 
ply of  oil.  Many  of  the  wells  and  lubricators  may  be  in- 
spected by  opening  a  cover  or  door,  or  moving  back  a  slide. 
Where,  however,  there  is  no  means  of  readily  accomplish- 
ing this  inspection,  sight  or  gage-glass  tubes  are  fitted  in 
which  the  height  of  lubricant  is  visible,  or  a  glass  window 
is  attached  to  the  wall  of  a  box  or  well.  Glass-bodied  lubri- 


54  LUBRICATING  BEARINGS 

cators  often  take  the  place  of  those  with  soiled  metal  bodies, 
in  places  where  they  are  permissible.  Occasionally  a  float 
gage  is  utilized  to  indicate  the  level  of  the  oil.  With  a  gear- 
box of  ample  capacity,  no  indicator  may  be  necessary,  since 
a  certain  amount  is  poured  in,  sufficient  to  last  for  so  many 
weeks  or  months ;  and,  in  the  case  of  some  ball-bearings,  a 
grease  supply  sufficient  for  a  year  or  so  is  put  in  and  the 
casing  closed  up. 

The  access  of  dirt  and  grit  is  guarded  against  by  using 
strainers  and  filters.  In  a  well  sytem  of  lubrication  the 
sediment  naturally  falls  to  the  bottom,  and  care  should  be 
taken  that  it  is  not  stirred  up  again ;  in  fact,  many  bearings 
embody  provision  for  keeping  the  sediment  in  such  a  way 
that  it  cannot  possibly  be  returned.  Drain-plugs  at  the  low- 
est position  provide  for  the  drawing-off  at  intervals.  When 
using  felt  pads,  there  is  opportunity  to  make  these  assist 
in  keeping  the  surfaces  clean  by  a  wiper-like  action  which 
prevents  access  of  foreign  particles  between  the  rotating 
or  sliding  faces.  The  amount  of  protection  which  must  be 
afforded  to  bearings  and  parts  depends  upon  the  nature  of 
the  processes  carried  on  in  the  shop.  Anything  in  the  way 
of  grinding  demands  rigorous  guarding  of  all  openings 
where  access  is  possible,  and  felt  pads  and  disks  are  used 
largely  for  such  purposes. 

Examples  of  Lubricating  Devices.  The  most  primitive 
mode  of  oiling  is  that  of  drilling  a  hole  and  pouring  oil  into 
it,  leaving  it  to  work  its  way  along  the  bearing.  An  ad- 
vance on  this  is  to  groove  the  bearing  so  that  distribution 
takes  place  properly,  and  supply  some  means  of  insuring 
a  constant  flow  of  oil.  A  simple  arrangement  consists  of 
a  wick  leading  from  the  bearing  to  a  small  reservoir  of  oil. 
Such  a  bearing  is  very  suitable  for  light  and  moderate 
duties,  and  will  run  for  a  long  period  without  attention, 
although  it  is  not  so  suitable  for  high-speed  shafts  which 
require  flushing  and  continual  movement  of  the  oil  to  make 
them  run  cool.  On  many  bushings  and  bearings  the  oil  is 
not  distributed  by  a  single  hole  and  groove  in  the  journal, 
but  instead  there  is  a  long  slot  and  several  holes  lead  from 


LUBRICATING  BEARINGS 


55 


it  to  the  bearing  surface.  This  is  convenient,  in  some  cases, 
especially  where  bearings  are  difficult  of  access,  and  where 
they  have  a  longitudinal  movement  which  would  bring  a 
single  feeding  opening  out  of  the  range  of  a  pipe.  Two 
holes  are  often  drilled  through  near  each  end  of  a  long 
bearing,  so  as  to  insure  a  distribution  from  both  ends. 

Thrust  journals  constructed  with  a  number  of  collars 
may  be  lubricated  on  the  separate  passage  system,  Fig.  1, 
a  hole  for  each  collar  leading  from  the  common  reservoir. 
This  example  is  taken  from  a  heavy  planing  machine  table- 


Fig.  1.     Thrust  Bearing  with  Oil  Supply  to  Each  Collar 

driving  screw;  the  illustration  also  shows  the  application 
of  a  trough  below  the  end  of  the  bearing  to  catch  waste,  a 
fitting  that  is  very  commonly  used  in  various  types  of 
screws  and  other  bearings  that  come  at  the  ends  of  fram- 
ings. Alternative  practice  is  to  cast  a  well  below  the  col- 
lars of  sufficient  width  to  include  them  all,  and  fill  this. 
The  collars  then  are  constantly  smeared,  avoiding  the  pos- 
sibility of  one  or.more  running  dry  due  to  the  hole  being 
blocked  with  some  foreign  substance,  as  may  happen  with 
the  arrangement  shown  in  Fig.  1. 

Lubrication  by  Felt  Pads.  Examples  of  various  methods 
of  applying  felt  pads  for  distribution  are  found  in  different 
machine  tool  designs,  the  felt  pads  being  used  either  alone, 
or  in  combination  with  grooves  in  the  bushing  or  on  the 


56 


LUBRICATING  BEARINGS 


shaft.  The  felt  not  only  insures  a  supply  of  oil  on  every 
part  of  the  journal  that  it  touches,  but  it  filters  the  oil  as 
well,  and  prevents  the  passing  of  grit  or  particles  of  metal. 
The  pads  are  fitted  into  slots  cut  in  boxes  or  bushings,  and 
either  dip  into  a  well,  or  are  simply  fed  through  holes  by  a 


Figs.    2    and    3.      Different    Applications    of    Pad    and    Reservoir 
Systems 


Fig.   4.     Pad    and    Reservoir   System    with    Supply   from    Side 

cam,  or  from  some  type  of  lubricator.  The  pad  is  often  let 
into  a  capacious  well  holding  sufficient  oil  to  last  for  a  long 
period  (Fig.  2)  with  provision  for  the  return  of  the  waste 
oil  by  a  channel  from  the  end  or  ends  of  the  bearings.  Figs. 
3  and  4  show  two  variations  in  practice,  the  first  having  a 
side  fed  well,  and  a  pad  contained  in  a  brass  holder  pressed 


LUBRICATING  BEARINGS 


57 


by  a  spring,  and  the  second  a  modified  arrangement,  with 
the  oiler  set  vertically.  This  disposition  is  sometimes  more 
convenient  for  certain  machines  than  placing  it  on  top  of 
the  bearing  cap,  and  there  is  the  advantage  that  grit  can- 
not reach  the  spindle,  as  it  may  when  the  supply  is  poured 
down  from  above.  Alternatively  to  the  fitting  of  a  pad, 
wicking  is  sometimes  adopted. 

In  Fig.  5  there  is  shown  a  form  of  construction  which 
has  been  adopted  for  bearings  used  to  support  horizontal 
and  vertical  driving  shafts  on  certain  machine  tools.  Oil 


HORIZONTAL  SHAFT 


VERTICAL  SHAFT 

Machinery 


Fig    5. 


Method    of    Lubricating    Horizontal    and    Vertical 
Machine   Tool    Driving   Shafts 


is  delivered  through  a  tube  which  carries  it  into  an  annular 
space  machined  in  the  outside  of  the  bronze  bearing  box, 
and  the  oil  flows  around  through  this  space  to  the  opposite 
side  of  the  box  from  the  point  at  which  the  delivery  tube 
is  connected.  Here  there  is  a  slot  cut  through  the  box  to 
communicate  with  the  inside  or  bearing  surface,  this  slot 
being  filled  with  felt.  The  oil  flows  through  the  felt  to  the 
bearing,  and  the  felt  serves  the  double  purpose  of  filtering 
impurities  from  the  oil  and  acting  as  a  wiper  which  dis- 
tributes the  oil  evenly  over  the  surface  of  the  bearing  which 
it  is  required  to  lubricate.  The  illustration  clearly  shows 
the  arrangement  of  this  simple  method  of  lubricating. 


58 


LUBRICATING  BEARINGS 


Ring  Oiling.  A  system  most  extensively  employed  for 
spindles  and  shafts  is  the  ring-oiling  method,  which  insures 
a  larger  flow  than  is  caused  by  the  pad  device.  This  method 
of  providing  for  automatically  delivering  oil  to  a  bearing 
requires  one  or  more  rings  which  are  hung  over  the  top  of 
each  journal  and  extend  down  sufficiently  below  the  journal 
at  the  under  side  so  that  they  dip  into  a  reservoir  filled  with 
oil.  'As  the  journal  rotates,  it  carries  the  rings  around, 
thus  bringing  the  portion  of  each  ring  which  was  formerly 
immersed  in  the  oil  up  into  contact  with  the  top  of  the 
journal.  The  ring  carries  a  considerable  amount  of  oil 


Fig.      6. 


Bearing    with    Two    Oiling    Rings    and    Height    Gage 
(A)    Perforated    Ring 


with  it,  and  in  this  way  a  constant  supply  of  oil  is  deposited 
on  the  journal. 

This  method  is  used  in  conjunction  with  a  reservoir  for 
each  bearing,  or  with  a  reservoir  or  box  common  to  several 
bearings.  If  a  gear-box,  for  example,  has  a  body  of  oil  into 
which  the  gears  run,  passages  can  be  arranged  to  lead  to 
the  bearing  wells,  which  simplifies  arrangements;  or  the 
bearings  may  be  constructed  in  a  self-contained  manner  if 
they  lie  out  of  the  plane  of  the  oil  box.  In  long  journals  it 
is  often  the  practice  to  employ  two  oiling  rings  to  provide 
greater  quantity  and  better  distribution  of  the  lubricant. 
An  instance  of  this  is  seen  in  Fig.  6,  which  also  illustrates 
the  gage-glass  fitted  to  observe  the  height  of  oil.  Sediment 


60  LUBRICATING  BEARINGS 

is  an  important  feature  on  the  bearings  of  any  grinding 
machine,  and,  in  addition  to  the  ring-oiled  radial  bearings, 
thrust  bearings  are  provided  to  support  the  load  which 
is  applied  in  an  endwise  direction.  This  combination  radial 
and  double  end  thrust  bearing  is  automatically  oiled. 

It  is  claimed  that  this  ring-oiling  device  is  so  efficient  in 
operation  that  the  spindle  literally  floats  on  an  oil  film, 
thus  greatly  reducing  the  amount  of  power  required  to 
drive  the  machine.  Tests  which  have  been  conducted  to 
determine  the  transmission  efficiency  of  these  ring-oiling 
bearings  are  said  to  have  shown  that  it  is  within  2  per  cent 
of  the  efficiency  of  ball  bearings.  In  the  operation  of  ring- 
oiled  bearings  of  this  type,  the  oil  should  be  drawn  off  about 
every  six  months,  the  exact  length  of  time  depending  upon 
the  conditions  of  service  under  which  the  bearings  are  op- 
erated. The  oil  wells  have  ample  capacity;  for  instance, 
on  the  No.  17  Besly  disk  grinder,  with  a  spindle  2i/2  inches 
in  diameter,  the  oil  wells  are  7  inches  deep.  Two  solid 
steel  rings  are  provided  for  each  bearing,  which  operate 
through  channels  cut  in  the  bearing  bushings  in  such  a  way 
that  it  is  impossible  for  a  ring  to  be  displaced  and  fail  to 
operate  properly.  The  bearing  boxes  are  split  to  facilitate 
assembly,  and  the  housings  in  which  these  boxes  are  in- 
serted are  so  arranged  that  replacement  of  the  boxes  is  an 
easy  matter  when  this  becomes  necessary.  A  special  grade 
of  phosphor-bronze  is  used  for  the  boxes,  and  they  are  de- 
signed with  ample  bearing  surface  so  that  there  is  very 
little  wear. 

On  disk  grinding  machines,  considerable  end  thrust  is 
set  up  when  work  is  forced  against  the  grinding  wheel,  and 
this  is  particularly  true  in  the  case  of  machines  furnished 
with  a  lever  feeding  mechanism  for  the  work-table.  On 
single-spindle  Besly  disk  grinding  machines  a  grinding 
wheel  is  mounted  at  both  ends  of  the  spindle,  which  makes 
it  necessary  to  design  the  bearings  in  such  a  way  that  pro- 
vision is  made  for  supporting  the  thrust  load  which  is  ap- 
plied in  both  directions.  It  is  also  important  to  work  out 
the  design  in  such  a  way  that  there  will  be  no  end  motion 


LUBRICATING  BEARINGS  61 

of  the  spindle  while  grinding,  because  this  would  prevent 
the  work  from  being  ground  accurately  to  size  and  would 
make  it  impossible  to  produce  duplicate  parts.  End  play  is 
taken  up  by  adjusting  collars  threaded  on  the  spindle  under 
the  flange  of  the  driving  pulley.  The  machine  can  be  safe- 
ly operated  without  any  end  play  in  the  spindle.  In  Fig. 
7  it  will  be  seen  that  end  thrust  is  supported  by  flanges 
A  and  B  of  the  right-hand  bearing  bushing.  Attention  is 
called  to  the  fact  that  this  bushing  is  made  in  two  parts, 
which  are  separated  at  C  with  sufficient  clearance  space, 
so  that  in  the  event  of  any  longitudinal  expansion  of  the 
bushing,  due  to  a  rise  in  temperature  during  operation  of 
the  bearing,  such  expansion  is  taken  up  in  the  clearance 
space  without  affecting  the  lateral  adjustment  of  the 
spindle ;  also,  there  will  be  no  tendency  f 01*  the  bushing  to 
swell  outward  along  the  spindle  and  bind  against  the  thrust 
collars  D  and  E,  which  are  located  at  opposite  ends  of  the 
radial  bearing  bushing.  Attention  is  called  to  the  fact  that 
the  bushing  is  anchored  in  the  head  of  the  grinding  ma- 
chine by  means  of  two  pins  F  and  G,  which  fit  into  holes 
that  are  slightly  elongated  to  permit  expansion  or  contrac- 
tion of  the  bushing  without  causing  any  unnecessary  strain. 
There  are  no  holes  through  the  caps  which  cover  each  of 
the  bearings  on  this  machine,  so  that  it  is  impossible  for 
grit  or  dirt  to  find  its  way  into  the  bearings. 

In  working  out  this  design,  an  interesting  method  has 
been  provided  for  lubricating  both  the  thrust  and  radial 
bearings.  Referring  first  to  the  detail  view  of  a  part  of 
the  bushing  which  is  shown  separately,  it  will  be  seen  that 
the  liner  H  is  set  back  in  order  to  form  an  oil-groove  along 
the  radial  bearing  at  both  sides  of  the  spindle.  These  oil- 
grooves  extend  to  the  end  of  the  bushing  and  then  in  an  out- 
ward direction  almost  to  the  periphery  of  the  flanges  on 
the  radial  bearing  which  engage  the  thrust  collars.  The 
thrust  faces  of  both  flanged  ends  of  the  right-hand  bearing 
bushing  are  grooved,  as  shown  at  7,  and  carry  oil  to  all 
parts  of  the  thrust  bearing.  The  groove  is  circular  in  form, 
but  eccentric  with  the  spindle,  and  it  is  made  of  such  diam- 


62 


LUBRICATING  BEARINGS 


eter  that  all  portions  of  the  face  of  each  hardened  thrust 
collar  which  bears  against  the  flange  on  the  radial  bear- 
ing pass  over  the  oil-groove  during  one  revolution  of  the 
spindle,  which  insures  oil  reaching  all  parts  of  the  thrust 
bearing.  Oil  is  also  delivered  to  this  groove  from  the  oil- 
grooves  formed  by  the  bushing  liners  H,  to  which  refer- 
ence has  already  been  made.  As  the  oil-grooves  in  the 
thrust  bearings  are  circular  in  form,  an  eccentric  with  the 
spindle  rotary  motion  of  the  thrust  collars  against  the  oil 
in  the  grooves  tends  to  circulate  this  oil  and  provide  a 
copious  flow  of  lubricant.  After  this  type  of  disk  grinder 


Fig.    8.      Showing    Lubrication    by    Chain    and    by    Spring 

spindle  bearing  was  adopted,  it  was  found  practicable  to 
increase  the  speed  75  per  cent  where  such  an  increase  was 
desirable. 

A  bearing  on  a  grinding  machine,  provided  with  a  chain- 
oiling  device,  is  shown  in  Fig  8.  The  view  shown  at  A 
represents  a  compromise  between  the  chain  and  the  solid 
ring — a  spiral  spring  looped  and  hooked  together  to  revolve 
with  the  shaft. 

Rings  for  Ring-oiling  Bearings.  The  great  variety  of 
rings  that  are  in  successful  use  would  appear  to  indicate 
that  the  section  of  the  ring  that  is  adopted,  has  little  to 
do  with  its  efficiency.  It  can  be  seen  that  a  ring  of  rela- 
tively heavy  section  will  be  less  likely  to  be  stopped  by  the 
oil  than  one  of  small  section  and  correspondingly  light 


LUBRICATING  BEARINGS  63 

weight.  Rings  and  oil  that  do  acceptable  work  after  being 
started  often  fail  to  start  satisfactorily  because  the  oil  is 
stiff  enough  to  overcome  the  very  slight  friction  that  exists 
between  the  shaft  and  the  ring.  This  point  should  be  con- 
sidered in  connection  with  the  size  of  the  oil  reservoir  and 
the  kind  of  oil  that  gives  most  satisfactory  results.  If  the 
reservoir  is  made  large  enough  to  provide  sufficient  oil 
storage  to  reduce  the  necessity  of  frequently  renewing  the 
oil,  and  the  ring  hangs  deep  in  it,  there  will  be  a  tendency 
to  retard  the  ring  when  the  reservoir  is  filled  to  its  capacity. 
Large  rings  have  a  smaller  area  in  contact  with  the  shaft, 
and  have  a  tendency  to  assume  a  position  oblique  to  the 
shaft  and  to  swing  laterally;  consequently  the  diameter  of 
the  rings  should  not  be  too  large. 

Chain  oiling  seems  to  offer  many  advantages  over  ring 
oiling,  but  the  cheapness  of  rings  and  the  fact  that  they 
give  satisfactory  service  in  millions  of  bearings,  appears 
to  be  sufficient  commendation  to  insure  keeping  them  in 
use.  Some  large  producers  of  ring  oiling  bearings  make 
all  their  rings  below  5  inches  in  diameter  out  of  seamless 
brass  tubing.  The  only  objection  to  this  material  is  that  a 
tube  is  occasionally  found  that  is  eccentric  enough  to  pre- 
vent satisfactory  action.  If  the  ring  is  very  slightly  out  of 
balance,  it  will  not  move  properly  and  fails  to  carry  oil  to 
the  bearing  in  a  satisfactory  manner. 

Fixed  Oiling  Rings  or  Disks.  With  the  ring-oiling  method 
previously  referred  to,  the  ring  is  hung  loosely  on  the 
spindle,  and  revolves  at  a  slow  rate.  If  it  is  fixed  to  run  at 
the  same  speed,  the  action  is  not  sufficiently  effective,  be- 
cause the  centrifugal  force  throws  the  oil  outward  and 
very  little  of  it  can  reach  the  shaft.  When  some  manner 
of  catching  or  scraping  the  oil  off  the  ring  is  included,  this 
arrangement  is  not  objectionable.  For  instance,  with  one 
arrangement,  the  fixed  ring  or  elevator  disk  throws  the  oil 
up  into  the  distributor  at  the  top,  whence  it  flows  along  slop- 
ing surfaces  which  communicate  by  vertical  holes  with  the 
top  of  the  bearing.  Some  high-speed  spindles  have  a  filter- 
ing arrangement  incorporated;  the  oil  is  thrown  by  the 


64 


LUBRICATING  BEARINGS 


disks  into  a  trough  at  the  top,  and  it  runs  along  this  into 
recesses  filled  with  filtering  material  through  which  no  for- 
eign particles  can  pass  into  the  bearings.  Instead  of  provid- 
ing a  gage-glass  for  inspection,  the  simpler  plan  of  screw- 
ing a  brass  window  plate  with  a  small  piece  of  glass  in- 
serted is  adopted.  The  oil-ring  scraping  method  is  repre- 
sented by  Fig.  9,  the  ring  being  keyed  to  the  shaft ;  at  the 
top  are  two  lugs  or  scrapers,  A,  with  only  sufficient  space 
between  them  for  the  ring  to  revolve.  The  result  is  that 
the  oil  raised  is  scraped  off  the  ring  and  thrown  into  the 
grooves  in  the  bearing. 


Fig.    9.      Ring    and    Scraper    Method    of    Lubrication    which    is 
sometimes    employed    with    Satisfactory    Results 

Oil  Conducted  by  Wicks.  Wicking  is  now  largely  utilized 
to  supply  bearings  in  a  manner  that  could  not  be  accom- 
plished by  pads,  or  at  least  not  so  well.  The  principle  is  to 
trail  the  piece  of  wick  in  the  oil  reservoir,  and  lead  it  from 
there  to  the  bearing  surface ;  this  is  a  very  elastic  principle, 
and  possesses  two  main  advantages.  One  is  that  the  oil  is 
filtered  and,  consequently,  no  dirt  is  transmitted  by  the 
wick ;  the  other,  that  a  feed  can  be  procured  from  a  well  or 
gear-box  not  necessarily  situated  close  to  the  bearing.  If  the 
wick  is  in  proper  condition,  and  the  oil  supply  is  maintained, 
there  is  no  risk  of  the  bearings  running  dry.  No  direct 
stream  of  oil  ever  reaches  the  bearings,  since  the  wicking 
is  arranged  in  such  a  fashion  that  the  oil  only  climbs  by 
capillary  attraction.  Fig.  10  represents  the  application  of 


LUBRICATING  BEARINGS 


65 


long  wicking  to  feed  two  bearings.  A  subsidiary  advantage 
of  wicking  is  that  it  can  be  employed  to  convey  oil  through 
a  hole  in  the  side  of  a  reservoir  or  cup  divided  by  a  parti- 
tion into  two  chambers.  One  of  these  is  never  opened  to 
the  air,  and  cannot  receive  flying  grit  or  dust  from  the  shop, 
but  only  forms  a  passage  to  lead  the  wick  to  the  bearing 
surfaces.  The  other  chamber  contains  the  wicking  coiled 


Fig.    10.  Reservoir  and    Long    Wick   serving   Two    Bearings 


Fig.   11. 


Lubrication  from    Inside  of  Shaft — a   Method  which  can 
be  used  to  Advantage  in   Many   Instances 


up  in  a  mass  to  absorb  oil,  and  the  communication  between 
the  chambers  is  such  that  no  direct  flow  can  occur  to  wash 
undesirable  substances  along. 

Special  Oil  Ducts.  There  are  numerous  instances  in 
which  the  difficulty  of  reaching  concealed  bearings  results  in 
the  adoption  of  special  pipings  or  passages.  The  advent  of 
all-geared  drives  for  speeds  and  feeds  greatly  complicated 
the  matter.  A  common  method  is  to  drill  a  longitudinal  hole 
in  the  shaft,  and  connect  radial  holes  with  this  to  lead  out 


66 


LUBRICATING  BEARINGS 


to  the  various  bearings  or  wheels.  Usually  the  lubricant  is 
supplied  through  the  shaft  end,  but  it  may  have  to  be  fed 
from  a  radial  or  inclined  hole  in  some  cases.  Fig.  11  is 
selected  to  illustrate  both  ways,  the  pinion  and  clutch  A 
and  B  receiving  oil  through  the  shaft  from  the  end  oiler, 
and  the  gear  C  its  supply  from  the  inclined  passage  fed 
from  the  piped  bearing  adjacent.  The  reason  for  turning 
the  semicircular  groove  in  the  shaft  at  the  place  where  B 
is  situated  is  that,  as  the  latter  does  not  revolve,  there 
would  be  no  opportunity  for  the  oil  to  spread  itself  circum- 
ferentially.  Fig.  12  shows  a  method  of  supply  to  a  fixed 
pin  on  which  is  a  pinion  and  a  distance  piece.  A  groove  is 


Figs.  12  and  13.     Special   Methods  of  Supplying  Oil 

turned  in  the  pin  where  it  rests  in  the  bearing  bracket,  and 
a  transverse  hole  leads  the  oil  from  this  to  the  central  pas- 
sage. In  places  where  it  is  not  feasible  to  lead  a  pipe  in 
from  above,  as  shown,  on  account  of  the  proximity  of  gears 
or  other  details,  a  lateral  pipe  can  be  inserted  (see  detail 
view,  Fig.  12)  to  fill  the  vertical  hole  up  which  the  oil  rises 
to  the  pin.  This  pipe  is  either  disposed  horizontally,  or 
slopes  down,  or,  if  a  head  is  available  from  a  well  or  tank 
or  pump  supply,  it  can  be  brought  up  from  below.  In  a 
few  instances  it  is  impracticable  to  conduct  oil  through  the 
center  of  a  spindle,  on  account  of  this  being  used  for  the 
passage  of  a  draw-rod  or  a  chuck  tube.  In  such  a  case,  a 
special  oil-hole  is  drilled,  Fig.  13,  in  the  metal  between  the 
central  hole  and  the  outside. 

Piping  for  Conducting  Lubricants.     The  combination  of 
holes  and  pipes  is  frequently  necessary;  sometimes  the  oil 


LUBRICATING  BEARINGS  67 

passes  for  a  certain  distance  through  a  hole  and  then  finishes 
its  journey  by  way  of  a  pipe  for  precision  of  location.  The 
ease  with  which  pipes  can  be  bent  and  carried  around 
angles  greatly  assists  in  their  disposition,  and  often  saves 
awkward  or  expensive  drilling.  Piping  is  largely  utilized- 
to  span  gaps  where  the  lubricant  could  not  be  supplied  with 
certainty,  and  without  waste,  to  the  interior  oil-hole. 

The  close  proximity  of  a  pulley  or  other  detail  often  ren- 
ders it  impracticable  to  reach  a  bearing  with  an  ordinary 
oil-can  spout,  so  the  plan  of  arranging  a  pipe  is  followed, 
the  top  being  closed  with  a  plug,  or  an  oiler.  When  a  num- 
ber of  such  pipes  have  to  be  used,  it  is  usually  best,  if  cir- 
cumstances allow,  to  bring  the  terminations  all  together 
at  one  spot,  not  necessarily  into  a  tank,  but  alongside  into 
a  holding  block,  and  thus  have  them  handy  for  attention. 

The  practice  of  covering-in  sets  of  gears  with  casings 
which  are  necessary  for  protective  purposes,  or  may  form 
an  integral  part  of  the  design  of  bearings  and  lever  anchor- 
ages, frequently  renders  some  amount  of  piping  necessary, 
to  lead  from  the  external  oilers  to  the  various  bearings. 
The  alternative  is  to  drill  the  shafts  and  convey  the  oil  by 
way  of  these,  but  it  is  sometimes  inconvenient  to  do  so. 
The  oil-pipe  either  leads  from  the  cover  to  the  bearing,  or 
hangs  some  little  way  off  and  lets  the  oil  drop  into  a  cupped 
hole,  or  a  raised  rim,  as  the  case  may  be.  Sometimes  a 
bushing  is  screwed  into  the  bearings  and  has  a  flanged  head, 
with  an  ample  bell-mouth,  to  catch  the  oil.  The  cover  can 
be  removed  and  replaced  without  disturbing  any  connec- 
tions, which  is  not  the  case  when  the  pipes  actually  enter 
the  bearings  and  fit  into  them. 

In  a  great  many  feed-gears  and  other  details,  it  is  im- 
possible to  apply  oil  directly  to  certain  of  the  bearings,  be- 
cause of  their  inaccessibility,  and,  in  such  cases,  it  is  often 
the  practice  to  provide  a  single  trough  on  the  top  of  a 
fixed  or  a  tumbler  casting,  and  drill  holes  and  fit  and  bend 
pipes  suitably  to  reach  the  other  bearings.  In  order  to 
prevent  waste  of  oil,  the  trough  is  sometimes  divided  by 
partitions,  thus  providing  each  leading-out  hole  with  its  own 


68 


LUBRICATING  BEARINGS 


receptacle.  When  a  tumbler  bearing  has  to  be  lubricated, 
the  feeding-in  should  be  so  arranged  as  to  avoid  loss  of  oil 
through  the  tumbler  moving  out  of  the  range  of  the  hole, 
or  pipe,  or  tray  from  which  it  drops.  This  is  done  by  cast- 
ing a  narrow  trough  of  appropriate  length  on  the  tumbler. 
Fig.  14  illustrates  a  common  design,  with  a  cup  on  the 
higher  bearing  communicating  by  a  groove  with  the  hole 


Figs.      14     and     15.       Tumbler 
Bracket    Troughs     and     Felt 
Pad    for   Slide 


Fig.    16.     Ordinary    Method    of 

Lubrication  of  Top  and  Bottom 

Vertical  Journals 


in  the  end  hole.  The  groove  comes  under  the  end  of  the 
pipe  through  which  the  oil  is  fed,  and  never  moves  out  of 
its  reach. 

In  some  of  the  more  complicated  designs  of  machines, 
special  provisions  are  necessary  to  lubricate  parts  that  are 
subject  to  frequent  change  of  position — slides  specifically. 
This  is  seen,  for  example,  in  the  portion  of  a  grinding  ma- 


LUBRICATING  BEARINGS 


69 


chine,  Fig.  17,  where  a  sloping  chute,  A,  receives  the  oil 
from  the  tube  and  oiler  in  the  slide  above,  and  conducts  it 
over  the  lip  of  the  bearing  to  the  vertical  shaft.  Any  alter- 
ation in  position  of  the  upper  slide  consequently  makes 
no  difference,  and  there  is  no  waste,  but  all  the  oil  from 
the  inlet  is  caught.  In  slides  not  suitably  provided  in  this 
manner,  it  may  be  essential  to  bring  them  to  a  definite 
position,  put  in  the  oil,  and  wait  for  a  certain  time  to  per- 


Fig.      17.      Arrangement   of   Trough    to   catch   Oil    from    Pipe    in- 
serted  in  a   Moving  Slide  above  the   Part  to  be  lubricated 

mit  it  all  to  escape.  In  this  illustration  the  bearing  for  the 
shaft  by  the  worm-wheel  is  lubricated  from  a  bent  pipe 
taken  to  the  outside  of  the  frame.  Another  illustration  of 
an  awkward  situation  is  seen  in  Fig.  18,  the  vertical  shaft 
obtaining  its  supply  from  the  pipe  above,  discharging  into 
the  groove  and  thence  to  the  bush  groove,  while  the  worm  is 
lubricated -from  a  combination  of  holes  and  pipes,  with  a 
trough  to  maintain  the  worm  in  oil  constantly.  Fig.  18,  at 
A,  shows  a  point  in  connection  with  the  conduction  of  oil 
through  slides,  from  an  upper  one  to  another ;  to  prevent  the 
oil  from  spreading  in  a  film  under  the  slides,  the  lower  face 


70 


LUBRICATING  BEARINGS 


is  counterbored  to  catch  the  drip  from  the  edges  of  the  hole 
and  lead  it  properly  into  the  continuation  hole. 

Lubrication  of  Flat  Sliding  Surfaces.  The  lubrication  of 
tables  presents  some  variations  in  methods  of  supply  and 
distribution.  A  great  deal  depends  upon  the  size  and 
weight  to  be  dealt  with,  and  upon  the  speed  of  movement, 
A  slow  moving  table  or  slide,  or  one  subject  only  to  occa- 


Fig.   18.     Conduction    by   Tubes,   Grooves   and    Passages 

sional  alterations  in  position  does  not  require  so  much 
lubricant  as  a  rapidly  moving  one  in  which  the  oil  is  swept 
off  more  quickly,  or  squeezed  out  by  pressure.  A  small 
table,  such  as  on  a  cutter  grinder,  for  instance,  can  be 
oiled  satisfactorily  enough  by  the  cam,  pouring  on  the  sur- 
faces while  the  table  is  run  back.  If  the  length  prevents 
this  being  done,  lateral  oil-holes  are  drilled,  and  vertical 
ones  to  communicate  with  the  under  side  of  the  table  face ; 


LUBRICATING  BEARINGS 


71 


or,  if  V-slides  are  used,  diagonal  holes  are  drilled.  Grooves 
or  pads  distribute  the  film  evenly  over  the  surfaces,  and 
pads  have  the  merit  of  retaining  a  portion  of  oil  and  keep- 
ing the  surfaces  moist  for  considerable  periods.  Several 
such  pads  can  be  inserted  in  pockets  in  the  slide  (see  sec- 
tional view,  Fig.  15),  and  the  oil  is  then  supplied  by  a  pass- 
age to  each  pad. 

The  location  of  the  oil-holes,  plugs,  or  oilers  is  a  matter 
of  importance  in  certain  types  of  tables.  In  some  grind- 
ing machines  there  is  no  objection,  for  instance,  to  drill- 
ing the  holes  vertically  from  the  table  top,  and  letting  in 


Fig.    19.      Lubricating    Rollers   for   Grinding    Machine 

plugs  or  spring  caps;  but  in  other  machines  these  areas 
might  be  covered  for  a  long  time  with  fixtures  or  other 
fittings,  and  there  would  be  no  chance  to  get  at  the  aper- 
tures without  removing  the  fixtures.  Then  the  lubrication 
might  be  neglected. 

The  most  effective  method  of  lubricating  a  heavy  table 
or  slide,  such  as  that  of  a  planer,  a  heavy  shaper,  grinder, 
or  a  boring  mill,  is  to  employ  rollers  sunk  into  oil-pockets, 
thus  forming  an  automatic  device  independent  of  the  care 
of  the  operator,  and  providing  a  supply  of  lubricant  at  each 
return  of  the  table,  or  as  fast  as  it  is  squeezed  out.  The 


72 


LUBRICATING  BEARINGS 


primitive  device  is  simply  to  float  a  wooden  roller  in  the 
oil-pocket,  but  it  should  have  some  means  of  attachment 
to  prevent  its  rising  unnecessarily  high  after  the  table  has 
passed.  Of  course,  in  rotating  tables,  as  in  boring  mills, 
a  roller  would  remain  in  the  same  position ;  but,  even  then, 
it  is  well  to  afford  a  definite  pressure  by  springs,  which 
will  result  in  proper  rotation  and  an  increase  in  the  amount 


Fig.  20.     Lubricating  Rollers  and  Well  for  Grinding   Machine, 
showing    Application    of    both    Plain    and    V-grooved    Roller 

of  oil  smeared  on.  Fig.  19  illustrates  the  type  of  roller 
fitting  used  in  a  type  of  grinding  machines,  for  the  flat  and 
the  V-ways,  respectively.  The  wheels  are  mounted  on  a 
cross-pin  held  in  a  central  plunger,  which  slides  up  and 
down  in  &  casing,  being  maintained  in  the  normal  position 
at  the  top  by  the  coiled  spring.  In  another  type,  frames 
similar  to  those  in  Fig.  20,  A  and  B,  are  used  to  lubricate 
the  tables  of  grinding  machines.  Studs  are  screwed  into 
bosses  at  the  ends  of  the  oil-pocket,  encircled  by  springs, 
and  receive  the  ends  of  the  frame  which  supports  the  roller. 


LUBRICATING  BEARINGS 


73 


This  construction  permits  the  plain  roller  (Fig.  20,  A)  to 
be  made  without  a  break  across  its  face.  Although  the 
V-wheels  do  not  reach  right  across  the  slope  of  the  vee, 
this  is  a  matter  of  no  consequence,  since  gravity  makes  up 
for  the  deficiency  in  this  respect. 

Slides  which  are  not  lubricated  across  their  bearing 
width  by  rollers  or  pads  require  grooves  to  distribute  the 
oil  properly.  The  aim  in  the  disposition  of  these  grooves 
is  to  spread  the  oil  nearly  across  the  width,  and  numerous 
methods  are  followed,  although  the  results  are  much  the 
same.  The  precise  arrangement  may  often  depend  upon  the 
position  and  number  of  the  oil-holes.  In  a  vertical  knee  or 


Fig.  21.     Various  Arrangements  of  Oil  Grooves  on  Flat  Surfaces 

slide,  with  a  single  oiler  at  the  center  of  the  top  edge,  the 
grooves  radiate  from  this  oiler  to  the  right  and  left.  Fig. 
21  gives  three  alternative  dispositions  for  milling-machine 
tables  moving  horizontally.  The  zig-zag  style  is  a  favorite 
one,  and  is  used  also  largely  on  the  bearing  surfaces  -of 
circular  tables  like  those  in  boring  mills,  carrying  a  suffi- 
cient supply  of  lubricant. 

Lubricating  Vertical  Spindles.  Vertical  spindles  present 
some  difficulties  in  regard  to  efficient  lubrication  which  do 
not  exist  in  horizontal  ones;  this  is  due  to  the  inevitable 
tendency  of  the  oil  to  run  down  and  out  of  the  bearings 
quickly.  Ring-oiling  is  out  of  the  question,  and,  if  a  consid- 
erable quantity  of  oil  is  required,  pads  must  be  used,  or  the 
oil  must  be  kept  in  constant  motion  and  supplied  by  helical 


74  LUBRICATING  BEARINGS 

raising  grooves.  An  ordinary  method  of  supply  is  adopted 
in  the  vertical  shaft  illustrated  by  Fig.  16 ;  the  oil  is  poured 
in,  on  the  removal  of  the  stopper,  both  through  the  central 
hole  and  around  the  top  of  the  shaft,  thence  flowing  by  the 
bearing  grooves  around  the  bottom  and  top  journals.  Wicks 
are  employed  extensively  to  conduct  and  distribute  oil  to  ver- 
tical bearings.  If  a  reservoir  of  oil  is  close  at  hand,  the  wick 
can  be  brought  direct  from  this,  and  piping  is  not  required. 
Felt  pads  are  also  used  to  retain  the  oil. 

Lubricating  Vertical  Grinding  Wheel  Spindle  Bearing.  In 
Fig.  22  there  is  shown  a  cross-sectional  view  of  the  wheel- 
head  of  a  Blanchard  belt-driven  vertical  surface  grinding 
machine;  and  the  design  of  the  bearings  for  carrying  the 
wheel  spindle,  together  with  the  means  provided  for  assur- 
ing efficient  lubrication,  will  undoubtedly  prove  of  interest. 
This  entire  wheel-head  is  carried  on  a  vertical  slide,  so  that 
alignment  of  the  spindle  bearings  is  made  entirely  indepen- 
dent of  the  slide.  There  are  ball  thrust  bearings  at  both  the 
lower  and  upper  ends  of  this  spindle ;  and  for  carrying  the 
radial  load  there  is  a  bronze  bearing  at  the  lower  end  of  the 
spindle  and  a  radial  ball  bearing  at  the  upper  end.  The 
great  advantage  of  ball  bearings  in  such  a  case  is  that  they 
may  be  packed  with  grease  and  housed  in  such  a  way  that 
the  grease  is  kept  in  the  bearing  and  adequate  protection 
is  afforded  against  the  entrance  of  grit  and  other  foreign 
matter,  which  would  abrade  the  bearings.  With  such  an  ar- 
rangement, the  bearings  require  practically  no  attention, 
provided  they  are  furnished  with  the  proper  kind  of  lubri- 
cant which  is  chemically  neutral;  that  is  to  say,  free  from 
both  acid  and  alkali.  Attention  is  called  to  the  hemispherical 
seats  on  the  races  of  the  ball  thrust  bearings  which  fit  corre- 
sponding surfaces  machined  to  receive  them.  It  is  the  pur- 
pose of  this  arrangement  to  have  the  hemispherical  surface 
on  the  race  adjust  itself  for  slight  inaccuracies  in  alignment 
or  to  compensate  for  slight  strains  which  develop  in  the 
wheel-head,  thus  enabling  the  bearing  to  distribute  the 
thrust  load  over  all  of  the  balls  and  assuring  efficient  trans- 
mission of  power. 


LUBRICATING  BEARINGS 


75 


At  the  lower  end  of  the  spindle  there  is  a  tapered  bearing 
which  is  arranged  with  the  large  end  of  the  taper  at  the  top, 
so  that  it  is  impossible  to  transmit  any  of  the  wheel  thrust 
to  this  bearing.  Tapered  bronze  bushing  A  can  be  easily 


SPINDLE  SUPPORTING 


U I 


STEEL  SAFETY 
GUARD 


Machinery 


Fig.  22. 


Provision  made  for  Lubrication  of  Spindle  Bearings 
of  Vertical  Surface  Grinding  Machine 


raised  by  turning  the  threaded  ring  B  to  provide  for  taking 
up  any  wear  which  develops  between  the  spindle  bearing  and 
its  bronze  box.  This  adjusting  ring  B  is  turned  by  a 
spanner  wrench  and  the  bronze  bushing  is  not  split.  The 
provision  of  means  for  delivering  lubricant  to  this  tapered 


76 


LUBRICATING  BEARINGS 


spindle  bearing  is  particularly  interesting.  Lubricant  is  de- 
livered to  an  oil  reservoir  C,  from  which  it  flows  down 
through  a  channel  cut  in  the  bronze  bushing  at  the  left-hand 
side  of  the  spindle  to  gain  access  to  the  spiral  oil-groove  which 
is  cut  in  the  journal.  Oil  is  carried  up  through  this  groove, 
and  in  this  way  a  liberal  supply  of  lubricant  is  always  dis- 
tributed over  the  bearing.  Upon  reaching  the  top  of  the 
bearing,  excess  oil  finds  its  way  into  channels  at  each  side  of 
the  spindle  and  flows  dowrn  through  these  channels  into 
reservoir  C,  where  it  is  available  for  subsequent  use.  By 


E 

1  - 

F 

I 

E 

Machinery 


Fig    23.      Lubricating    Arrangement    for    a    Gear    within    a 
Housing 

studying  the  direction  of  flow,  which  is  indicated  by  arrows 
shown  in  this  illustration,  the  reader  will  easily  obtain  a  per- 
fectly clear  idea  of  the  way  in  which  oil  circulates  through 
this  bearing. 

The  upper  end  of  the  spindle  carries  a  threaded  collar 
with  springs  D  beneath,  which  press  up  against  it  with  a 
force  exceeding  the  weight  of  the  revolving  parts  by  at 
least  five  hundred  pounds.  By  this  means,  the  thrust  bear- 
ing at  the  lower  end,  on  which  depends  the  accuracy  of  the 
grinding,  is  always  kept  tight.  All  backlash  in  the  spindle 
is  eliminated  and  variations  of  spindle  length  with  temper- 
ature are  automatically  corrected.  The  downward  reaction 


LUBRICATING  BEARINGS 


77 


of  the  springs  is  carried  on  a  ball  thrust  bearing  in  the 
upper  box,  and  side  pull  at  that  point,  due  to  the  belt,  is 
taken  on  a  radial  ball  bearing. 

Provision  for  Grease  Lubrication.  Fig.  23  illustrates  pro- 
vision for  grease  lubrication  of  a  shaft  which  is  journaled 
in  a  fixed  frame  and  which  has  a  gear  B  independently  re- 
volvable  on  shaft  A  (in  a  reverse  direction  to  that  of  the 
shaft)  and  housed  within  a  casing  C.  Rings  D  are  turned 
on  the  shaft  for  the  double  purpose  of  taking  up  end  thrust 


/ 


Y////A 


\ 

\  '/  I 

Y////A 


Y/////A 


Machinery 


Fig.  24.      Exampl^  of   Multiple   Capillary   Lubrication 

and  of  confining  the  grease  which  is  fed  between  them  from 
the  cups  E.  Grease  is  also  fed  from  the  cup  F  into  groove 
G,  whence  it  passes  through  holes  provided  in  the  groove  to 
the  conductor  H,  drilled  along  the  center  of  the  shaft,  the 
grease  being  forced  out  through  the  outlet  /  into  the  bearing 
of  the  gear. 

Multiple  Capillary  Lubrication.  An  example  of  multiple 
capillary  lubrication  for  inaccessible  bearings  is  shown  in 
Fig.  24.  The  bearings  A,  B,  and  C  are  supplied  with  oil 
from  a  tank  by  means  of  the  copper  tubes,  D,  E,  and  F,  re- 
spectively, which  are  packed  lightly  with  cotton  wicking. 
The  tubes  extend  well  into  the  tank  as  may  be  seen,  and  are 
securely  fastened  in  the  bearings  by  swaging  them  into 
holes  provided  for  this  purpose.  It  is  necessary  to  swage 


78 


LUBRICATING  BEARINGS 


the  tubes  into  the  bearings  in  order  to  provide  an  air-tight 
connection.  It  is  not  essential  that  the  wicking  should 
touch  the  shaft,  although  it  should  extend  very  close  to  it. 
The  tubes  should  be  fastened  to  the  bearings  at  an  angle  of 
90  degrees  with  the  pressure  sides,  with  reference  to  the 
direction  of  rotation  of  the  shaft,  as  shown  by  the  arrow. 

Types  of  Self-oiling  Bearings.  The  so-called  "self-oil- 
ing" type  of  bearings  may  work  on  either  of  two  principles : 
Oil  may  be  taken  from  a  reservoir  and  carried  up  to  the 
bearing  by  any  suitable  means,  or  the  bearing  box  which 


Machinery 


Fig.   25.      Self-oiling   Type   of    Bearings   where    Lubrication   is 
effected  by  Capillary  Action 

surrounds  the  journal  may  be  impregnated  with  some  form 
of  lubricant.  The  latter  type  of  bearing  is  often  referred  to 
as  an  "oilless  bearing,"  although  in  many  cases  it  is  found 
desirable  to  give  bearings  of  this  type  perhaps  25  per  cent 
of  the  quantity  of  oil  which  would  be  required  for  the  effi- 
cient operation  of  a  bearing  of  standard  design.  The  great 
advantage  of  self -oiling  or  oilless  bearings  is  that  they  do 
not  require  as  much  attention  as  the  ordinary  type,  and  in 
the  event  of  neglect  to  supply  such  bearings  with  the  quan- 
tity of  lubricant  which  they  are  expected  to  receive,  they 
are  capable  of  operating  for  a  considerable  length  of  time 
without  serious  damage. 

Dodge  Capillary  Self-Oiling  Bearing.    In  Fig.  25  there  is 
shown  what  is  known  as  a  capillary  type  of  self -oiling  bear- 


LUBRICATING  BEARINGS 


79 


ing,  which  is  suitable  for  use  in  lineshaft  hangers  and  sim- 
ilar types  of  equipment.  This  bearing  is  made  by  the  Dodge 
Mfg.  Co.,  of  Mishawaka,  Ind.  The  bearing  box  has  been 
designed  with  an  opening  at  the  bottom,  in  which  there  is 
inserted  a  wooden  block  that  extends  down  through  the  box 
for  a  sufficint  distance  so  that  the  lower  side  of  the  block 
can  dip  into  an  oil  reservoir  provided  in  the  bearing  hous- 
ing. The  block  is  held  against  the  shaft  by  a  spiral  spring, 
and  it  has  a  series  of  slots  sawed  in  it  which  come  to  a  sharp 
angle  at  one  end.  It  is  the  tendency  of  the  oil  to  rise  in  the 


Machinery 


Fig.  26. 


Diagram    illustrating   Principle   governing   Operation 
of  Capillary   Bearing 


narrow  end  of  these  slots  in  the  wooden  block,  as  a  result 
of  capillary  action,  which  is  responsible  for  carrying  oil  up 
to  the  bearing. 

Perhaps  a  better  idea  of  the  arrangement  will  be  secured 
after  referring  to  Fig.  26,  which  shows  a  cross-sectional 
view  of  the  wooden  block,  illustrating  the  way  in  which  it 
is  slotted,  and  a  cross-sectional  view  through  the  bearing 
showing  how  the  oil  is  drawn  up  in  the  narrow  side  of  these 
slots  in  the  wooden  block,  due  to  the  capillary  action  which 
has  just  been  mentioned.  A  uniform  film  of  oil  is  main- 
tained on  the  shaft  in  this  way,  and  oil-grooves  are  cut  in 
the  bearing  box  in  order  that  these  grooves  may  be  kept 
full  of  oil,  thus  facilitating  lubrication  of  the  bearing.  As 
there  is  no  mechancial  agitation  of  the  oil  contained  in  the 


80  LUBRICATING  BEARINGS 

reservoir  in  this  bearing,  any  foreign  matter  which  is  pres- 
ent in  the  oil  is  allowed  to  settle  to  the  bottom,  so  that  only 
pure  oil  is  admitted  to  the  bearing  and  no  trouble  is  experi- 
enced through  grit  or  other  foreign  materials  rapidly  wear- 
ing the  bearing  surfaces.  The  reservoir  in  this  bearing 
has  sufficient  capacity  to  contain  a  supply  of  oil  which  is 
adequate  to  keep  the  bearing  efficiently  lubricated  for  a 
period  of  six  months.  Before  replenishing  the  supply  of 
oil,  the  bearing  should  be  thoroughly  cleaned,  and  this  re- 
sult is  easily  accomplished  by  removing  the  drain  plug  at 
the  bottom  of  the  reservoir  and  flushing  the  entire  bearing 
with  kerosene,  after  which  the  plug  is  replaced  and  a  fresh 
supply  of  oil  placed  in  the  bearing. 

Bronze  Bushing  with  Provision  for  Automatic  Lubrication. 
Another  type  of  self-oiling  bearing  is  shown  in  Fig.  27, 
which  is  especially  adapted  for  use  in  loose  pulleys  and 
similar  installations  where  it  is  desirable  to  have  the  combi- 
nation of  a  bronze  bearing  box  and  provision  for  automatic 
lubrication.  This  bearing  is  made  by  the  Moccasin  Bush- 
ing Co.,  of  Chattanooga,  Tenn.  It  will  be  seen  in  the  illus- 
tration, which  shows  the  method  of  mounting  this  bearing, 
that  an  oil  reservoir  is  provided  in  the  hub  of  the  loose 
pulley,  and  the  principle  by  which  lubrication  is  effected  is 
quite  similar  to  that  of  the  bearing  furnished  with  a  wick, 
through  which  oil  is  drawn  by  capillary  action.  Moccasin 
bushings  can  be  used  in  any  type  of  machine  member 
furnished  with  an  oil  cavity  from  which  lubricant  can  be 
drawn  by  the  capillary  oil-feeders  which  are  contained  in 
holes  that  pass  transversely  through  the  bushing  so  that 
they  come  into  contact  with  the  bearing  surface  in  the 
manner  shown  on  the  inside  of  the  bushing.  They  deliver 
a  continuous  supply  of  oil  to  the  bearing,  and  are  so  pre- 
pared that  they  cannot  glaze  or  clog.  It  is  claimed  that 
these  bearings  prevent  the  waste  of  oil,  in  addition  to 
supplying  the  bearing  with  exactly  the  desired  volume  of 
oil  which  is  required  for  its  efficient  operation. 

Oil  Baths  for  Submerging  Bearing  Surfaces.  Submerged 
lubrication,  that  is  by  running  parts  in  a  bath  of  oil  or 


LUBRICATING  BEARINGS 


81 


grease  which  they  continually  stir  up  and  spread  over 
themselves,  exists  in  many  forms.  In  the  oil  bath  as  cor- 
rectly arranged,  there  is  never  any  lack  of  lubricant  and 
the  chief  care  is  to  see  that  no  sediment  is  thrown  up,  or 
that  any  parts  are  shielded  from  the  spread  of  oil.  The 
familiar  worm-gear  and  spiral  gear  drive  running  in  an  oil 
trough  was  followed  by 
the  geared  drives  in 
which  other  classes  of 
gears  are  caused  to  dip 
in  oil  and  splash  it  over 
the  teeth.  Fast-running 
gears  necessitate  com- 
plete covering  to  pre- 
vent the  oil  from  flying 
out  of  the  box;  but,  in 
worm-gears,  it  is  not 
always  necessary  to  af- 
ford absolute  protec- 
tion, as,  for  instance, 
where  the  trough  is 
situated  within  a  fram- 
ing, and  dust  or  grit 
cannot  enter.  A  half- 
trough  is  all  that  is 
then  required.  When, 
however,  the  box  is  sit- 
uated in  the  open,  complete  enclosure  is  usually  desirable. 
The  action  of  gears  running  in  an  oil  bath  can  be  some- 
times utilized  to  lubricate  the  adjacent  bearings  as  well,  in 
place  of  fitting  separate  oilers  to  these.  Care,  however,  must 
be  taken  that  these  bearings  receive  a  sufficient  amount, 
which  is  not  always  the  case  in  badly  designed  boxes.  The 
oil  which,  is  thrown  up  by  centrifugal  force  to  the  roof  of 
the  box  may  have  to  be  deflected  by  various  arrangements 
so  as  to  direct  it  into  the  oil  recesses  above  the  bearings. 
Sometimes  a  passage  is  made  in  the  casting  to  lead  down 
to  these  points,  or  ribs  are  cast  or  screwed  on  to  catch 


Machinery 


Fig.  27.      Bronze   Bushing   provided  with 

Means  of  automatically  drawing  Oil 

from     Supply     Reservoir 


82  LUBRICATING  BEARINGS 

the  flying  oil  and  let  it  run  down  and  drip  at  the  place 
required,  without  actually  confining  it  in  grooves;  or  a 
piece  of  piping,  or  bent  wire  may  be  fitted  and  arranged 
to  accomplish  a  similar  function.  Occasionally,  a  strip  of 
metal  is  attached  and  sloped  in  such  a  manner  that  the  oil 
is  thrown  against  it,  and  thence  off  at  an  angle  to  the  bear- 
ing, or  to  a  channel  communicating  with  it. 

The  ideal  method  of  lubrication  for  the  bearings  in  gear- 
boxes on  machine  tools  and  other  bearings,  where  such  an 
arrangement  is  possible,  is  to  have  the  gears  run  in  a 
reservoir  filled  with  oil.  This  not  only  avoids  excessive 
wear  of  the  gear  teeth,  but  it  also  provides  for  ample  lub- 
rication of  the  bearings  by  the  splash  system  of  lubrication. 
Oil-holes  may  be  provided  at  the  top  of  the  bearings,  so 
that  oil  thrown  from  the  gears  drops  into  these  holes  and 
provides  a  continuous  flow  of  lubricant  through  the  bear- 
ings. Where  this  arrangement  is  employed,  an  ample 
amount  of  lubricant  can  be  put  into  the  reservoir  to  last 
for  several  weeks,  the  length  of  time  being  governed  by 
the  conditions  of  service.  A  gage-glass  on  the  reservoir 
shows  the  level  of  the  oil,  and  at  infrequent  intervals  it  is 
merely  necessary  to  replenish  the  supply  of  oil.  When 
gears  are  running  in  mesh,  or  when  a  shaft  is  rotating  in 
its  bearing,  the  effect  of  friction  is  to  tear  off  very  fine 
fragments  of  metal  which  collect  in  the  oil  in  such  a 
reservoir;  also,  there  is  a  tendency  for  a  "muck"  to  collect 
in  the  bottom  of  the  reservoir,  due  to  oxidation  of  the  oil. 
For  these  two  reasons,  and  also  owing  to  certain  other 
causes,  it  is  necessary  to  clean  out  the  oil  reservoirs  at 
intervals  of  about  six  months.  To  facilitate  this  cleaning 
process,  a  drain  plug  should  always  be  provided  at  the 
bottom  of  the  reservoir  which  can  be  screwed  out  in  order 
to  drain  off  the  dirty  oil.  The  reservoir  should  then  be 
flushed  out  with  kerosene  to  clean  away  all  accumulations 
of  metal  particles  and  oxidized  oil,  after  which  the  drain 
plug  is  replaced  and  the  reservoir  refilled  with  clean  oil. 

Bearings  Oiled  by  the  Splash  System.      An    example    of 
the  splash  method  of  lubrication  is  shown  in  Fig.  28,  which 


LUBRICATING  BEARINGS 


83 


illustrates  the  table  gear  bracket  of  the  vertical  surface 
grinding  machine.  By  building  this  mechanism  as  an  inde- 
pendent unit,  the  process  of  manufacture  is  simplified,  in 
addition  to  making  provision  for  the  efficient  lubrication  of 
the  gears  and  bearings  by  application  of  the  splash  system 
of  oiling.  The  drive  is  transmitted  through  a  spline  shaft 
A  and  bevel  gears  to  the  table  gear  B.  Oil  is  retained  in 
reservoir  C  at  the  level  indicated  by  shaded  lines,  and  the 
bearing  of  the  spline  shaft  is  lubricated  by  the  ring-oiling 
principle,  which  will  be  more  fully  discussed  in  connection 
with  another  example  of  bearing  design.  By  this  method, 


FELT  PACKING 


RING  OILING  BEARING 


SPLINE  SHAFT 


Machinery 


Fig  28.     Method   of   lubricating   Table   Gear   Bracket  of  Ver- 
tical   Surface    Grinding    Machine 

ring  D  runs  over  the  bearing  to  be  lubricated  and  its  lower 
side  dips  into  the  oil  carried  in  reservoir  C.  Rotation  of 
the  shaft  results  in  continuously  turning  ring  D,  with  the 
result  that  oil  is  carried  up  by  the  ring  and  deposited  at 
the  top  of  the  bearing,  thus  delivering  a  constant  supply  of 
lubricant  to  the  bearing.  A  felt  packing  E  is  employed  to 
exclude  abrasive  dust,  which  would  soon  wear  out  the 
bearing  if  special  precautions  were  not  taken  to  prevent 
it  from  getting  between  the  rubbing  surfaces;  and  tele- 
scopic tubes  form  an  effective  seal  at  the  right-hand  end  of 
the  shaft.  When  it  is  required  to  clean  out  reservoir  C  by 
the  method  which  has  already  been  explained,  drain  plug 
F  is  withdrawn  in  order  to  provide  for  the  escape  of  dirty 


84  LUBRICATING  BEARINGS 

oil  from  the  reservoir,  and  the  flushing  out  of  the  reservoir 
with  kerosene  so  as  to  remove  all  accumulated  foreign 
matter  before  a  fresh  supply  of  lubricant  is  added. 

For  lubricating  the  bearing  of  the  vertical  shaft  carrying 
gear  B,  oil  is  delivered  through  channels  communicating 
with  a  felt  packing  G  which  is  in  contact  with  the  bearing 
of  the  vertical  shaft.  This  packing  serves  the  double  pur- 
pose of  carrying  a  continuous  supply  of  oil  to  the  bearing 
and  filtering  out  any  foreign  matter  with  which  the  oil  may 
have  become  contaminated.  Any  excess  oil  which  passes 
through  this  bearing  is  caught  in  the  lower  reservoir  and 
replenishes  the  supply  of  oil  for  lubricating  the  gears  and 
the  ring-oiled  bearing  of  the  horizontal  shaft.  Felt  pack- 
ings are  very  generally  used  in  this  way  to  provide  for  de- 
livering clean  oil  to  bearings  of  grinding  machines  and 
similar  equipments  where  the  bearings  are  so  situated  that  it 
is  difficult  to  exclude  abrasive  dust  and  other  substances  that 
would  rapidly  score  and  wear  out  the  bearings  if  they  came 
in  contact  with  the  rubbing  surfaces. 

Flooded  Lubrication.  Pump  systems  embody  many  ar- 
rangements of  a  varied  character  for  the  thorough  dis- 
tribution of  the  lubricant.  In  the  most  complete  gear- 
boxes, and  in  some  machines — notably  all-geared  milling 
machines — the  same  supply  is  utilized  to  flood  the  gears 
and  bearings,  being  pumped  up  from  the  well  at  the  base 
and  falling  from  a  perforated  pipe  in  cascades  on  the  gears, 
while  suitably  arranged  pipes  conduct  it  into  the  bearings. 
The  top  part  of  each  bearing  is  cast  as  a  trough,  and  the 
one  below  it  catches  the  oil  that  runs  out  from  the  ends  or 
center  hole  of  the  bearing.  Grooves,  holes,  chutes,  and  pipes 
are  employed  to  assist  in  the  conduction. 

When  geared  feed-boxes  were  first  developed  for  use  on 
"Milwaukee"  milling  machines  built  by  the  Kearney  & 
Trecker  Co.,  Milwaukee,  Wis.,  it  soon  became  apparent 
that  in  order  to  give  efficient  service,  the  gear-boxes  would 
have  to  be  provided  with  some  means  of  continuous  lubrica- 
tion. After  studying  the  merits  of  various  methods,  the 
design  finally  adopted  consisted  in  constructing  oil-tight 


LUBRICATING  BEARINGS 


85 


boxes,  so  that  the  gears  dipped  into  the  oil.  This  result 
proved  so  satisfactory  that  attention  was  turned  to  the  idea 
of  adopting  a  geared  spindle  drive,  but  to  accomplish  this 
result  the  gears  had  to  be  placed  one  above  the  other,  thus 
precluding  the  possibility  of  having  all  of  the  gears  dip  into 
an  oil  bath.  Finally,  provision  was  made  for  lubrication 
by  having  the  gears  placed  one  above  the  other  and  deliver- 
ing oil  to  the  top  gear  by  means  of  a  pump  drawing  its 


Machinery 


Fig.  29     Provision  for  delivering  Continuous  Stream  of  Oil  to 
All    Bearings  and   Gears   in    Milling    Machine    Drive 

supply  from  a  reservoir,  as  shown  in  Fig.  29  at  A,  and  de- 
livering the  oil  through  holes  in  pipe  B.  While  in  opera- 
tion, a  gallon  of  oil  per  minute  floods  down  over  the  gears 
and  bearings.  At  the  top  of  each  bearing  there  is  a  cup 
which  catches  part  of  the  oil  thrown  by  the  gears  and  allows 
it  to  run  down  through  a  duct  to  the  bearings.  In  this  way, 
both  the  gears  and  bearings  are  kept  thoroughly  lubricated, 
so  that  efficient  transmission  of  power  is  obtained  and  wear 


86  LUBRICATING  BEARINGS 

is  reduced  to  practically  the  absolute  minimum.  In  ordi- 
nary practice,  the  oil-grooves  are  closed  at  the  ends  to 
prevent  the  escape  of  oil  from  the  bearings,  but  in  the 
present  case  the  grooves  are  cut  right  through  to  provide  for 
a  free  circulation  of  oil  and  the  washing  away  of  all  for- 
eign substances  from  the  bearings. 

On  20-inch  all-geared  drilling  machines  built  by  the 
Barnes  Drill  Co.,  Rockford,  111.,  all  bearings,  with  the  ex- 
ception of  the  spindle  sleeve  and  cross-spindles,  are  con- 
tinuously oiled  by  an  automatic  lubrication  system.  Oil  is 
delivered  by  a  geared  pump  in  the  reservoir  of  the  machine 
and  distributed  constantly  to  all  gears  and  bearings,  includ- 
ing the  crown  gears  and  feed-box.  This  automatic  lubrica- 
tion system  is  manufactured  under  license  from  the  Kearney 
&  Trecker  Co.  A  close  view  of  the  mechanism  of  one  of  the 
Barnes  drilling  machines  is  shown  in  Fig.  30,  and  the 
geared  pump,  which  is  driven  by  the  constant-speed  driving 
shaft,  will  be  seen  at  the  bottom  of  the  oil  reservoir.  Oil  is 
drawn  into  this  pump  through  a  strainer,  which  is  also 
located  at  the  bottom  of  the  reservoir,  although  it  is  not 
shown  in  the  illustration.  There  is  a  valve  which  can  be  set 
with  just  enough  resistance  to  lift  the  required  volume  of 
oil  to  the  crown  gear  bearings,  while  the  remainder  of  the 
oil  overflows  directly  into  the  oil-hole  for  the  rear  bearing. 
The  pipe  which  will  be  seen  just  underneath  the  "back- 
bone" of  the  machine,  leading  up  to  the  crown  gears,  has 
small  holes  drilled  in  it  just  above  each  of  the  bearings  in 
order  that  oil  may  escape  to  provide  for  the  constant  lubri- 
cation of  bearings  on  both  of  the  diagonal  shafts.  A  groove 
is  cut  inside  of  each  double  bearing  which  leads  the  oil 
across  to  the  lower  diagonal  shaft.  A  sufficient  volume  of 
oil  is  delivered  to  the  crown  gear  housing  so  that  the  over- 
flow runs  into  the  feed-box,  from  which  it  works  down 
through  the  worm-shaft  bearing,  and  in  so  doing  oils  the 
worm  and  worm-wheel,  after  which  it  is  led  back  into  the 
frame  of  the  machine  and  cascades  back  to  the  original 
reservoir.  In  this  way,  every  bearing,  aside  from  the 
spindle  sleeve  and  cross-spindle  bearings,  is  automatically 
supplied  with  a  constant  stream  of  oil. 


LUBRICATING  BEARINGS 


87 


Elevated  Oil  Tanks.  In  very  large  machines,  when  a 
considerable  quantity  of  oil  has  to  be  flooded  through  bear- 
ings and  over  surfacs,  a  head  is  sometimes  obtained  by  the 
use  of  an  elevated  tank,  from  which  pipes  lead  down  to  the 
various  grooves  or  passages.  The  pump  then  replenishes 


Fig.  30.     Provision  for  Continuous  Lubrication  of  Gears  and 
Bearings    on    Vertical    Drilling    Machine 

the  tank  a.t  the  required  rate,  the  oil  being  filtered  before 
returning.  Any  blocking  of  the  long  pipes  should  be  pro- 
vided against  by  the  inclusion  of  pet-cocks  at  suitable  posi- 
tions, close  to  the  bearings,  so  that  the  position  of  an  ob- 
struction can  be  discovered.  Apart  from  this  method  of 
obtaining  a  large  supply,  the  tank  is  also  often  embodied 
in  portions  of  machines  to  feed  certain  details  that  are 


88 


LUBRICATING  BEARINGS 


either  inaccessible  by  an  oil-can,  or  are  too  numerous  for 
individual  attention,  and  there  is  thus  risk  of  neglect.  The 
oil  either  runs  direct  to  the  places  needed,  or  is  fed  slowly 
by  siphon  wicks.  So  long  as  the  tank  is  filled,  kept  clean 
from  grit  or  dirt,  and  the  wicks  are  fitted  properly,  no 
trouble  can  ensue.  Fig.  31  illustrates  a  typical  case,  where 
all  the  oiling  orifices  are  located  close  together,  and  the 
pipes  from  the  trough  do  not  need  to  be  carried  far.  As 
the  trough  is  enclosed  inside  a  column  closed  by  the  flap 
door  no  lid  is  needed  to  cover  the  oil,  but  this  would  be  re- 
quired if  the  trough  were  situated  externally. 


Fig.  31.     Trough   and   Pipes  supplying  Several    Bearings  located 
in  Proximity  to  each  other 

Oiling  Lineshaft  Hanger  Bearings.  In  shops  where  the 
equipment  is  quite  congested,  it  is  likely  to  be  found  that 
there  is  danger  of  accidents  to  men  whose  duty  it  is  to  oil 
the  bearings  of  linshaft  hangers,  countershafts,  and  similar 
equipment  where  the  bearings  are  placed  in  somewhat  in- 
accessible positi6ns.  A  little  time  given  to  the  subject  of 
devising  methods  of  lubrication  may  often  bexthe  means  of 
saving  serious  accidents  and  consequent  litigation  over  em- 
ployer's liability.  Observation  of  the  following  points  will 
often  result  in  saving  trouble:  Wherever  possible,  the 
work  of  oiling  bearings  in  lineshaft  hangers  and  counter- 
shafts should  be  done  while  the  machinery  is  not  running. 
A  better  plan  is  to  equip  such  bearings  with  automatic 
lubricators  which  need  to  be  filled  only  at  infrequent  in- 
tervals ;  with  bearings  of  this  type,  it  is  always  feasible  to 


LUBRICATING  BEARINGS  89 

arrange  to  replenish  the  supply  of  lubricant  at  some  time 
when  the  machines  are  at  rest.  It  will  always  happen, 
however,  that  certain  conditions  will  arise,  making  it  nec- 
essary for  shafting  to  require  attention  while  the  machines 
are  running,  and  to  meet  such  contingencies,  safe  means  of 
access  must  be  provided,  among  which  mention  is  made  of 
the  following  : 

Where  ladders  are  used  to  reach  lineshafts  and  counter- 
shafts, they  should  be  provided  with  hooks  or  hangers  to 
fit  over  the  shaft  at  the  upper  end  and  spurs  at  the  lower 
end,  which  will  insure  obtaining  a  secure  grip  on  the  floor. 
With  such  provision,  there  is  no  likelihood  of  a  ladder 
slipping  and  causing  the  workman  to  be  thrown  into  mov- 
ing parts  of  a  machine.  In  big  shops  it  will  sometimes  be 
found  feasible  to  have  a  service  platform  or  "runway" 
provided  with  guard  rails  and  toe-boards  running  parallel 
to  lineshafts,  so  that  any  point  on  the  shaft  is  readily  ac- 
cessible. Moving  parts  of  machinery  should  not  be  allowed 
to  project  over  such  a  runway,  but  if  such  a  condition  is 
unavoidable,  the  moving  part  should  be  completely  enclosed. 
In  some  plants,  use  is  made  of  a  car  hung  from  an  I-beam 
running  parallel  to  the  lineshaft,  and  with  such  an  equip- 
ment the  oiler  can  readily  move  along  the  shaft  to  reach  all 
of  the  bearings.  The  use  of  such  a  car  or  of  the  service 
platform  is  naturally  restrictd  to  quite  large  shops.  Some 
shops  have  their  men  use  forced-feed  oil-cans  of  sufficient 
length  so  that  they  can  be  operated  from  the  floor. 

Where  men  are  employed  to  look  after  the  work  of  inspect- 
ing and  oiling  shafting  and  other  equipment  before  the 
regular  starting  time  of  the  plant,  accidents  sometimes 
happen  through  the  engineer's  starting  up  the  machinery 
before  these  men  have  finished  their  work.  This  source  of 
danger  can  be  overcome  by  providing  disconnecting  appli- 
ances which  make  it  possible  to  cut  out  any  section  of  the 
equipment  until  the  work  of  oiling  bearings  has  been  com- 
pleted. Switches  used  for  this  purpose  should  be  provided 
with  padlocks,  so  that  they  can  be  locked  in  either  the 
open  or  closed  position.  If  such  appliances  are  not  in- 


90  LUBRICATING  BEARINGS 

stalled,  it  is  good  practice  to  require  a  man  employed  in 
oiling  equipment  to  report  personally  to  the  engineer  of 
the  plant  that  he  is  going  to  oil  certain  machinery. 
Probably  the  best  safeguard  in  the  lubrication  of  bearings 
used  in  all  inaccessible  equipment  is  to  adopt  the  use  of 
one  of  the  so-called  "self-oiling"  types  of  bearings  which 
can  be  furnished  with  a  supply  of  lubricant  that  is  adequate 
for  a  considerable  period  of  time.  Bearings  of  this  type  are 
furnished  with  means  of  drawing  oil  from  the  reservoir 
and  delivering  it  to  the  bearing  surface,  so  that  constant 
and  efficient  lubrication  is  assured. 

Oil  Grooves  for  Bearings.  In  order  to  provide  for  uni- 
form distribution  of  oil  over  the  entire  surface  of  a  journal 
bearing,  it  is  common  practice  to  cut  what  are  termed  "oil- 
grooves"  in  the  surface  of  either  the  journal  or  its  box. 
These  grooves  are  usually  made  in  the  form  of  a  spiral  or 
some  kind  of  an  endless  curve,  as  shown  in  Fig.  32,  which 
illustrates  bearing  boxes  made  by  the  Bunting  Brass  & 
Bronze  Co.,  Toledo,  Ohio.  Special  machines  are  made  for 
cutting  oil-grooves,  which  provide  for  handling  this  work 
in  a  more  expeditious  manner  than  is  possible  with  hand 
tools  or  on  machine  tools  of  standard  design.  There  are 
several  reasons  for  cutting  oil-grooves  in  the  form  of 
spirals  or  other  curved  shapes,  instead  of  adopting  the 
practice  of  cutting  straight  grooves  parallel  to  the  axis  of 
the  journal.  If  such  a  practice  were  followed,  there  would 
be  a  tendency  for  oil  to  gather  in  the  grooves  near  the 
bottom  of  the  box,  while  those  on  the  sides  and  top  would 
remain  empty.  With  oil-grooves  of  spiral  or  similar  form, 
however,  this  trouble  is  not  experienced  and  rotation  of  the 
journal  has  the  further  tendency  of  circulating  the  oil 
through  these  curved  grooves,  thus  greatly  facilitating 
distribution  of  the  lubricant.  The  oil  should  be  introduced 
at  that  point  where  the  forces  acting  tend  to  separate  the 
shaft  and  box.  At  this  point  grooves  must  be  cut  in  the 
surface  of  the  box,  so  as  to  distribute  the  lubricant  evenly 
over  the  entire  length  of  the  journal.  Having  been  so  in- 
troduced and  distributed,  the  oil  will  adhere  to  the  journal, 


LUBRICATING  BEARINGS 


91 


and  be  carried  around  by  it  as  it  revolves  to  the  point 
where  it  is  pressed  against  the  box  with  the  greatest  force, 
thus  forming  the  lubricating  film  which  separates  the  rub- 
bing surfaces.  The  supply  of  lubricant  thus  continually 
furnished,  and  swept  up  to  the  spot  where  it  is  needed,  must 
not  be  diverted  from  its  course  in  any  way.  A  sharp  edge 


M//\V'/       \V/\Kf/ 
/  (   '  \         )  (    II  \ 


Fig.    32. 


Examples    of    Bronze    Bearing    Bushings    showing 
Different  Forms  of  Oil-grooves 


at  the  division  point  of  the  box  will  wipe  it  off  the  journal 
as  fast  as  it  is  distributed,  or  a  wrongly  placed  oil  groove 
will  drain  it  out  bfore  it  has  entirely  accomplished  its  pur- 
pose. As  generally  cut,  oil  grooves  have  two  faults;  first, 
they  are  so  numerous  as  to  cut  down  to  a  serious  extent  the 
area  of  the  bearing,  and,  second,  they  are  so  located  as  to 
allow  the  oil  to  drain  out  of  the  bearing.  As  few  grooves 
should  be  used  as  possible. 


92  LUBRICATING  BEARINGS 

Two  classes  of  bearings  which  may  well  be  made  without 
oil  grooves  are,  first,  the  cross-head  slippers  of  engines, 
and,  second,  crankpin  boxes.  The  cross-head  slipper  should 
have  a  recess  cut  at  each  end,  in  the  same  way  as  the  count- 
erboring  of  the  two-part  box.  The  best  way  to  oil  a  crank- 
pin  is  through  the  pin  itself.  In  the  case  of  overhung  pins, 
a  hole  is  drilled  lengthwise  of  the  pin  to  its  center.  A  second 
hole  is  drilled  from  the  surface  of  the  pin  to  meet  the  first 
one.  A  shallow  groove  should  now  be  cut  in  the  surface 
of  the  pin,  parallel  to  its  axis,  and  reaching  almost  to  the 
ends  of  the  bearing.  No  grooves  should  be  cut  in  the  boxes, 
but  the  edges  where  they  come  togethr  should  be  counter- 
bored.  As  much  care  and  attention  should  be  given  to  the 
oil  grooving  as  to  the  size  of  a  bearing,  yet  it  is  a  matter 
often  left  to  the.  fancy  of  the  mechanic  who  fits  it.  The 
purpose  of  the  grooves,  to  distribute  the  oil  evenly,  should 
ever  be  kept  in  mind,  and  no  groove  should  be  cut  which 
does  not  accomplish  this  purpose,  except  it  be  to  return 
waste  oil  to  a  place  where  it  may  again  be  of  use.  As  a 
rule,  bearings  have  too  many  grooves  and,  far  from  assist- 
ing the  lubricants,  they  generally  drain  the  oil  from  where 
it  is  most  needed. 


CHAPTER  IV 
DESIGN  OF  PLAIN  BEARINGS 

THE  design  of  journals,  pins,  and  bearings  of  all  kinds 
is  one  of  the  most  important  problms  connected  with 
machine  construction.  It  is  a  subject  upon  which  there  is, 
unfortunately,  conflicting  data.  The  results  obtained  from 
the  rules  given  by  different  engineers  will  be  found  to  differ 
by  60  per  cent  or  more.  Many  of  the  best  modern  engines 
have  been  designed  in  defiance  of  the  generally  accepted 
rules  on  this  subject,  and  many  other  engines,  when  pro- 
vided with  what  were  thought  to  be  very  liberal  bearing 
surfaces,  have  proved  unsatisfactory.  This  confusion  has 
largely  been  the  result  of  a  misconception  of  the  actual 
running  conditions  of  bearing. 

In  working  out  the  design  of  journal  bearings  for  use  on 
any  type  of  machine,  it  is  necessary  for  careful  consider- 
ation to  be  given  to  the  conditions  of  service  under  which 
each  bearing  will  operate.  This  is  particularly  true  in  the 
case  of  bearings  used  on  machine  tools,  because  there  is  a 
great  amount  of  variation  in  the  conditions  which  machine 
tool  bearings  are  required  to  fulfill.  In  bearings  for  driv- 
ing shafts,  provision  made  for  the  efficient  transmission  of 
power  and  freedom  from  wear  are  usually  the  two  points 
of  maximum  importance ;  but  in  the  main  spindle  bearings, 
these  important  points  may  receive  consideration  only  after 
provision  has  been  made  in  the  design  to  assure  obtaining  a 
bearing  which  will  be  a  tight  running  fit  when  new  and  in 
which  means  are  provided  to  compensate  for  any  wear  that 
may  develop  after  the  machine  is  placed  in  service.  Lost 
motion  in  -a  spindle  bearing  will  show  itself  by  the  presence 
of  chatter  marks  on  the  work  and  by  difficulty  experienced 
in  holding  dimensions  of  the  work  within  the  required 
limits  of  accuracy.  On  this  account,  the  designer  of  machine 

93 


94  DESIGN  OF  PLAIN  BEARINGS 

tool  spindle  bearings  must  first  consider  the  conditions 
under  which  the  bearings  are  to  operate  with  the  idea  of 
fulfilling  these  requirements  without  tendency  for  the  bear- 
ings to  wear  excessively. 

After  this  has  been  done,  it  is  necessary  to  take  steps  to 
work  out  the  design  along  such  lines  that  convenient  means 
are  provided  for  readily  taking  up  any  small  amount  of 
wear  which  may  develop  in  the  bearings.  Only  after  pro- 
vision has  been  made  for  maintaining  an  accurate  fit  be- 
tween the  spindle  and  its  bearings  can  the  designer  turn  his 
attention  to  the  question  of  transmission  efficiency,  al- 
though this  condition  must  also  be  fulfilled.  There  are  often 
special  conditions  which  must  be  considered  in  designing 
bearings  in  order  to  assure  satisfactory  operation.  For 
instance,  on  grinding  machines,  trouble  would  almost  surely 
be  experienced  through  abrasive  dust  from  the  wheel  find- 
ing its  way  into  the  bearings  and  causing  them  to  wear  ex- 
cessively, unless  the  housings  were  designed  with  special 
provision  to  exclude  dust  and  other  foreign  matter  from 
the  bearings.  This  is  an  example  of  special  conditions  likely 
to  require  careful  consideration  in  working  out  the  design 
of  bearings  capable  of  giving  satisfactory  service. 

General  Principles  Covering  Bearing  Design.  A  journal 
should  be  designed  of  such  a  size  and  form  that  it  will  run 
cool,  and  with  practically  no  wear.  The  question  of  both 
heating  and  wear  is  one  of  friction,  and  in  order  to  under- 
stand the  principles  upon  which  the  design  of  bearings 
should  be  based,  the  underlying  principles  of  friction  must 
first  be  understood.  Friction  is  defined  as  that  force  acting 
between  two  bodies  at  their  surface  of  contact,  when  they  are 
pressed  together,  which  tends  to  prevent  their  sliding  one 
upon  the  other.  The  energy  used  in  overcoming  this  force 
of  friction  appears  at  the  rubbing  surfaces  as  heat,  and  is 
ordinarily  dissipated  by  conduction  through  the  two  bodies. 
The  force  of  friction,  and  hence  the  amount  of  heat  gener- 
ated under  any  given  circumtsances,  can  be  greatly  reduced 
by  the  introduction  of  an  oily  or  greasy  substance  between 
the  rubbing  surfaces.  The  oil  or  grease  seems  to  act  in  the 


DESIGN  OF  PLAIN  BEARINGS  95 

same  way  that  a  great  number  of  minute  balls  would,  reduc- 
ing the  friction  and  wear,  and  thus  preventing  the  overheat- 
ing  and  consequent  destruction  of  the  parts.  On  this  account, 
all  bearings  are  always  lubricated.  Thus  the  question  of 
journal  friction  involves  the  question  of  lubrication. 

For  the  purpose  of  understanding  as  far  as  possible  what 
goes  on  in  a  bearing,  and  the  amount  and  nature  of  the 
forces  acting  under  different  conditions,  several  machines 
have  been  designed  to  investigate  the  matter.  In  general, 
they  are  so  arranged  that  a  journal  may  be  rotated  at  any 
desired  speed,  with  a  known  load  upon  the  boxes.  Suitable 
means  are  provided  for  measuring  the  force  of  friction  and 
also  the  temperature  of  the  bearing.  From  investigations 
with  such  apparatus,  it  has  been  found  that  the  laws  of  fric- 
tion of  lubricated  journals  differ  very  materially  from  those 
commonly  stated  in  text-books  as  the  laws  of  friction. 

Frictional  Resistance  in  Lubricated  and  Unlubricated 
Bearings.  It  is  generally  stated  that  the  force  of  friction 
is  proportional  to  the  force  with  which  the  rubbing  surfaces 
are  pressed  together,  doubling,  or  trebling,  as  the  case  may 
be,  with  the  normal  pressure.  This  law  is  perfectly  true 
for  all  cases  of  unlubricated  bearings,  or  for  bearings  lubri- 
cated with  solid  substances,  such  as  graphite,  soapstone, 
tallow,  etc.  When,  however,  the  bearing  is  properly  lu- 
bricated with  any  fluid,  it  is  found  that  doubling  the  pres- 
sure does  not  by  any  means  double  the  friction,  and  when 
the  lubricant  is  supplied  in  large  quantities,  by  means  of  an 
oil  bath  or  a  force  pump,  the  friction  will  scarcely  increase 
at  all,  even  when  the  pressure  is  greatly  increased.  From 
the  experiments  of  Thurston,  and  also  of  Tower,  it  appears 
that  the  friction  of  a  journal  per  square  inch  of  bearing 
surface,  for  any  given  speed,  is  equal  to: 

f  =  kp"  (1) 

where  /  =.the   force  of   friction   acting   on   every   square 

inch  of  bearing  surface; 
p  =  the  normal  pressure  in  pounds  per  square  inch 

on  that  surface; 
k  =  a  constant. 


96  DESIGN  OF  PLAIN  BEARINGS 

The  exponent  n  depends  on  the  manner  of  oiling,  and 
varies  from  1,  in  the  case  of  dry  surfaces,  to  0.50,  in  the 
case  of  drop-feed  lubrication;  0.40  or  thereabouts  in  the 
case  of  ring-  and  chain-oilers  and  pad  lubrication;  and  be- 
comes zero  in  case  the  oil  is  forced  into  the  bearing  under 
sufficient  pressure  to  float  the  shaft. 

The  second  law  of  friction,  as  generally  stated,  is  that  the 
force  of  friction  is  independent  of  the  velocity  of  rubbing. 
This  law  also  is  true  for  unlubricated  surfaces,  and  for  sur- 
faces lubricated  by  solids.  In  the  case  of  bearings  lubri- 
cated by  oil,  the  friction  increases  with  the  speed  of  rubbing, 
but  not  at  the  same  rate.  Expressed  as  an  equation : 

/  =  kv™  (2) 

where  /  =  the  force  of  friction  at  the  rubbing  surfaces  in 

pounds  per  square  inch ; 
re  =  a  constant ; 
v  =  the  velocity  of  rubbing  in  feet  per  second. 

The  exponent  m  varies  from  zero,  in  the  case  of  dry  sur- 
faces, to  0.20,  in  the  case  of  drop-feed,  and  0.50,  in  the  case 
of  an  oil  bath. 

The  third  law  of  friction,  as  it  is  generally  stated,  is  that 
the  friction  depends,  among  other  things,  on  the  composition 
of  the  surfaces  rubbed  together.  This,  again,  while  true  for 
unlubricated  surfaces,  is  not  true  for  other  conditions.  No 
matter  whether  the  surfaces  be  steel,  brass,  babbitt,  or  cast 
iron,  so  long  as  they  are  perfectly  smooth  and  true,  they 
will  have  the  same  friction  when  thoroughly  lubricated. 
The  friction  will  depend  upon  the  oil  used,  not  on  the  ma- 
terials of  journal  or  boxes,  when  the  other  conditions  of 
speed  and  pressure  remain  constant.  Many  people  think 
that  babbitt  has  less  friction  than  iron  or  brass,  under 
the  same  circumstances,  but  this  is  not  true.  The  reason 
for  the  great  success  of  babbitt  as  an  "anti-friction"  metal 
depends  upon  an  entirely  different  property,  as  will  be  ex- 
plained later. 

Combining  into  one  equation  the  different  laws  of  the 
friction  of  lubricated  surfaces : 

/  =  fatW  (3) 


DESIGN  OF   PLAIN  BEARINGS  97 

where  /  =  the  force  of  friction  at  the  rubbing  surface  in 

in  pounds  per  square  inch ; 

k  =  a  constant,  which  varies  with  the  excellence  of 
the  lubricant  from  0.02  to  0.04. 

The  other  quantities  are  as  before.  From  this  expression 
it  is  evident  that  the  friction  increases  with  the  load  on  the 
bearing,  and  also  with  the  velocity  of  rubbing,  although 
much  more  slowly  than  either. 

Generation  of  Heat  in  Bearings.  The  quantity  of  heat 
generated  per  square  inch  of  bearing  area,  per  second,  is 
equal  to  the  force  of  friction  times  the  velocity  of  rubbing. 
All  of  this  heat  must  be  conducted  away  through  the  boxes 
as  fast  as  it  is  generated,  in  order  that  the  bearing  shall  not 
attain  a  temperature  high  enough  to  destroy  the  lubricating 
qualities  of  the  oil.  The  hotter  the  boxes  become,  the  more 
heat  they  will  radiate  in  a  given  time.  When  the  bearing 
is  running  under  ordinary  working  conditions,  it  will  warm 
up  until  the  heat  radiated  equals  the  heat  generated,  and  the 
temperature  so  attained  will  remain  constant  as  long  as  the 
conditions  of  lubrication,  load,  and  speed  do  not  change. 
This  rise  in  temperature  above  that  of  the  surrounding  air 
varies  from  less  than  10  to  nearly  100  degrees  F.,  and  is 
commonly  about  30  degrees  F.  The  force  of  friction  or  the 
velocity  of  rubbing,  or  both,  must  be  kept  down  to  that  point 
where  the  temperature  shall  not  attain  dangerous  values. 
As  has  been  shown  in  the  preceding  paragraph,  it  was  for- 
merly believed  that  the  force  of  friction  was  equal  to  a 
constant  times  the  bearing  pressure,  and,  therefore,  that  the 
work  of  friction  was  equal  to  this  constant  times  the  pres- 
sure, times  the  velocity  of  rubbing.  Now,  since  it  is  the 
work  of  friction  that  must  be  limited  to  a  certain  definite 
value  per  square  inch  of  bearing  area,  it  has  been  concluded 
that  a  bearing  would  not  reach  a  dangerous  temperature 
if  the  product  of  the  bearing  pressure  per  square  inch  and 
the  velocity  of  rubbing  did  not  exceed  a  certain  value.  The 
limiting  value  for  the  product  of  pressure  and  velocity  is, 
therefore,  determined  by  Thurston's  formula: 

pv  =  C  (4) 


98  DESIGN  OF  PLAIN  BEARINGS 

in.  which  p  •=  bearing  pressure,  in  pounds  per  square  inch ; 
v  =  velocity  of  rubbing,  in  feet  per  second. 
C  =  constant   having   values   varying   from    800 
foot-pounds  per  second,  in  the  case  of  iron 
or  low-carbon  steel  shafts,  to  2600  foot- 
pounds,  in   the   case   of  high-carbon   steel 
crankpins. 

This  formula  is  satisfactory  for  bearings  running  at  ordi- 
nary speeds,  although  it  must  be  modified  for  extreme  cases. 

The  results  obtained  from  the  machines  for  testing  bear- 
ings are  very  even  and  regular  for  ordinary  pressures  and 
temperatures,  but  when  either  of  these  is  increased  to  a 
high  point,  the  friction  and  wear  of  the  bearing  suddenly 
increases  enormously.  The  reason  is  that  the  oil  has  been 
squeezed  out  of  the  bearing  by  the  great  pressure.  This 
squeezing  out  of  the  oil  and  consequent  great  increase  in  the 
friction  has  three  effects.  The  absence  of  the  lubricant 
causes  the  parts  to  scratch  or  score  each  other,  thus  rapidly 
destroying  themselves,  the  great  increase  in  friction  results 
in  a  sudden  very  high  temperature,  in  itself  destructive  to 
the  materials  of  the  bearing,  and  the  heating  is  generally 
so  rapid  as  to  cause  the  pin  and  the  interior  parts  of  the  box 
to  expand  more  rapidly  than  the  exterior  parts,  thus  causing 
the  box  to  grip  the  pin  with  enormous  pressure.  When  the 
oil  has  been  squeezed  out  in  this  manner,  the  bearing  is  said 
to  "seize." 

Influence  of  Quality  of  Oil.  The  unit  pressure  which 
any  bearing  will  stand  without  seizing  depends  upon  its  tem- 
perature and  the  kind  of  oils  used.  The  lower  the  tempera- 
ture of  the  bearings,  the  greater  the  allowable  unit  pressure. 
The  reason  for  this  is  that  oils  become  thinner  and  more 
free-flowing  at  the  higher  temperatures,  consequently  they 
are  more  easily  squeezed  out  of  the  bearing,  and  it  is  more 
likely  to  seize.  On  this  account,  the  higher  the  velocity  of 
rubbing,  the  less  the  unit  pressure  that  can  be  carried,  but 
it  does  not  follow  that  the  allowable  unit  pressure  varies 
inversely  as  the  speed  of  rubbing,  as  was  formerly  thought. 
The  thicker  and  less  free-flowing  an  oil  is,  the  greater  the 


DESIGN  OF  PLAIN  BEARINGS 


99 


unit  pressure  it  will  stand  in  a  bearing  without  squeezing 
out.  A  watch  oil  or  a  light  spindle  oil  can  be  used  only  under 
a  very  small  unit  pressure.  Sometimes  they  are  squeezed 


Bearing-  Pressures  for  Various  Classes  of  Bearings 
(Kimball  and  Barr) 


Class  of  Bearing  and   Condition   of  Operation 


Allowable 
Bearing    Pres- 
sure,  Lb.   per 
Sq.    In. 


naval  practice 
merchant  practice 


Bearings  for  very  slow  speed  as  in  turntables 
in  bridge  work 

Bearings  for  slow  speed  and  intermittent  load  as 
in  punch  presses 

Locomotive    wrist-pins    

Locomotive    crankpins    

Locomotive    driving    journals 

Railway  car  axles 

Marine  engine  main  bearings.    -! 

Marine    engine    crankpins 

Stationary  engine  main  bearings    j  for  dead  load* 

(high  speed)  |  for  steam  load 

Stationary  engine  crankpins    (  overhung  crank 

(high  speed)  "j  center   crank 

Stationary  engine  wrist-pins    (high  speed) 

Stationary   engine  main  bearings  (  for  dead  load* 

(slow  speed)  j  for  steam   load 

Stationary  engine  crankpins    (slow  speed) 

Stationary  engine  wrist-pins    (slow   speed) 

Gas  engines,  main  bearings 

Gas    engines,    crankpins 

Gas   engines,   wrist-pins 

Heavy  lineshaft  brass  or  Babbitt  lining 

Light  lineshaft  cast-iron  bearing  surfaces 

Generator  and  Dynamo  bearings 


7000  to  9000 


3000  to 

3000  to 

1500  to 

190  to 

300  to 

275  to 

400  to 

400  to 

60  to 

150  to 

900  to 

400  to 

1000  to 

80  to 

200  to 

800  to 

1000  to 

500  to 

1500  to 

1500  to 

100  to 

15  to 

30  to 


4000 

4000 

1700 

220 

325 

400 

500 

500 

120 

250 

1500 

600 

1800 

140 

400 

1300 

1500 

700 

1800 

2000 

150 

25 

80 


*Weight  of  shaft,   flywheels,  et< 


out  of  the"  bearing  when  the  pressure  does  not  exceed  50 
pounds  per  square  inch.  A  cylinder  oil  of  good  body  will 
stand  a  pressure  of  over  2000  pounds  per  square  inch  in 
the  same  bearing.  It  is  important  to  determine,  if  possible, 
in  each  case,  what  quality  of  oil  is  best  adapted  to  each  par- 


100  DESIGN  OF  PLAIN  BEARINGS 

ticular  bearing.  A  third  cause  influencing  the  pressure 
which  may  be  carried  is  adhesiveness  between  the  oil  and 
the  rubbing  surfaces.  Some  oils  are  more  certain  to  wet 
metal  surfaces  than  are  others,  and,  in  the  same  way,  some 
metals  are  more  readily  wet  by  oil  than  are  others.  It  is 
evident  that  when  the  surfaces  repel,  rather  than  attract, 
the  oil,  the  film  will  be  readily  broken  down,  and,  when  the 
opposite  is  the  case,  the  film  is  easily  preserved. 

Calculating  Bearing  Dimensions.  The  durability  of  the 
lubricating  film  is  affected  in  great  measure  by  the  character 
of  the  load  that  the  bearing  carries.  When  the  load  is  un- 
varying in  amount  and  direction,  as  in  the  case  of  a  shaft 
carrying  a  heavy  flywheel,  the  film  is  easily  ruptured.  In 
those  cases  where  the  pressure  is  variable  in  amount  and 
direction,  as  in  railway  journals  and  crankpins,  the  film  is 
much  more  durable.  When  the  journal  rotates  through  only 
a  small  arc,  as  with  the  wrist-pin  of  a  steam  engine,  the  cir- 
cumstances are  most  favorable.  It  has  been  found  that 
when  all  other  circumstances  are  exactly  similar,  a  car 
journal,  where  the  force  varies  continually  in  amount  and 
direction,  will  stand  about  twice  the  unit  pressure  that  a 
flywheel  journal  will,  where  the  load  is  steady  in  amount  and 
direction.  A  crankpin,  since  the  load  completely  reverses 
for  every  revolution,  will  stand  three  times,  and  a  wrist-pin, 
where  the  load  only  reverses  but  does  not  make  a  complete 
revolution,  will  stand  four  times  the  unit  pressure  that  the 
flywheel  journal  will. 

The  amount  of  pressure  that  commercial  oils  will  endure 
at  low  speeds  without  breaking  down  varies  from  500  to 
1000  pounds  per  square  inch,  where  the  load  is  steady.  It 
is  not  safe,  however,  to  load  a  bearing  to  this  extent,  since 
it  is  only  under  favorable  circumstances  that  the  film  will 
stand  this  pressure  without  rupturing.  On  this  account, 
journal  bearings  should  not  be  required  to  stand  more  than 
two-thirds  of  this  pressure  at  slow  speeds,  and  the  pressure 
should  be  reduced  when  the  speed  increases.  The  approxi- 
mate unit  pressure  which  a  bearing  will  endure  without  seiz- 
ing is  as  follows : 


DESIGN   OF  PLAIN  BEARINGS  10X 

PK 

P=  (5) 

DN  +  K 
in  which  p  =  allowable  pressure  in  pounds  per  square  inch 

of  projected  area; 
D  =  diameter  of  bearing  in  inches ; 
N  =  number  of  revolutions  of  journal  per  minute; 
P  =  maximum  safe  unite  pressure  under  given 
circumstances  at  slow  speed.  Ordinarily 
the  value  of  P  is  200  for  collar  thrust  bear- 
ings; 400  for  shaft  bearings;  800  for  car 
journals ;  1200  for  crankpins ;  and  1600  for 
wrist-pins.  Under  exceptional  circum- 
stances, these  values  may  be  increased  by  as 
much  as  50  per  cent,  but  only  when  the 
the  workmanship  is  the  best  and  the  care 
of  the  bearing  the ^ most  skillful;  in  addi- 
tion, a  bearing  should  be  readily  accessible 
and  the  oil  of  the  best  quality  and  unusually 
viscous.  Only  in  the  case  of  very  large  ma- 
chinery having  expert  supervision,  can 
these  higher  values  be  safely  adopted; 
K  =  quantity  depending  on  method  of  oiling,  etc. 
Its  value  may  be  assumed  for  ordinary 
work,  drop-feed  lubrication,  as  700;  first- 
class  care,  drop-feed  lubrication,  1000;  for 
force-feed  lubrication  or  ring  oiling,  from 
1200  to  1500;  extreme  limit  for  perfect  lu- 
brication and  air-cooled  bearings,  2000. 
The  value  of  2000  is  seldom  used  except 
in  locomotive  work  where  the  rapid  circu- 
lation of  the  air  cools  the  journals.  Higher 
values  than  2000  may  be  used  only  in  the 
case  of  water-cooled  bearings. 

Formula  (5)  is  in  a  convenient  form  for  calculating 
journals.  In  case  the  bearing  is  some  form  of  sliding  shoe, 
the  quantity  240  V  should  be  substituted  for  the  quantity 
DN,  V  being  the  velocity  of  rubbing  in  feet  per  second. 


102  DESIGN   OF  PLAIN   BEARINGS 

There  are  a  few  cases  where  a  unit  pressure  sufficient  to 
break  down  the  oil  film  is  allowable.  Such  cases  are  the 
pins  of  punching  and  shearing  machines,  pivots  of  swing 
bridges  and  similar  constructions,  where  the  motion  is  slow 
and  heating  cannot  well  result.  In  such  cases,  pressures  up 
to  4000  pounds  per  square  inch  are  permissible. 

High-speed  Bearings.        In    carefully    lubricated    high- 
speed bearings,  very  high  unit  pressures  are  permissible. 
The  following  figures  represent  the  practice  of  a  large  con- 
cern building  electrical  machinery  in  large  units : 
Velocity  in  feet  per  second  of 

rubbing  surfaces   20       30       40       60       75 

Permissible  pressure  in  pounds 

per  square   inch    165     190     205     225     230 

The  permissible  pressures  here  increase  with  the  speed. 
The  reason  for  this  is  that  the  higher  the  surface  speed,  the 
more  effectively  is  the  lubricant  dragged  in  against  the  hy- 
draulic pressure  due  to  the  load  carried,  the  high-speed  bear- 
ing acting  in  a  measure  as  a  pump  for  its  lubricant. 

Diameter  of  Shaft  or  Pin.  The  diameter  of  a  shaft  or  pin 
must  be  such  that  it  will  be  strong  and  stiff  enough  to  carry 
the  load.  In  order  to  design  it  for  strength  and  stiffness, 
the  approximate  length  must  be  known.  This  will  be  as- 
sumed from  the  following  equation : 

20  W  V~AT 

L  = (6) 

PK 

in  which  L  =  length  of  bearing  in  inches ; 

W  '-=  total  load  upon  bearing  in  pounds ; 

N  =  number  of  revolutions  of  journal  per  minute; 

P  and  K  =  same  quantities  as  in  Equation  (5). 

When  the  approximate  length  has  been  found  by  the  use 
of  this  equation,  the  diameter  of  the  shaft  or  pin  may  be 
found  by  the  general  formulas  for  the  strength  of  materials. 
The  length  of  the  journal  must  then  be  recomputed  by  the 
formula  given  in  the  next  paragraph. 

Length  of  Bearing.  Having  obtained  the  proper  di- 
ameter, a  bearing  length  must  be  selected  long  enough  so 


DESIGN  OF  PLAIN  BEARINGS  103 

that  the  unit  pressure  shall  not  exceed  the  required  value. 
This  length  may  be  found  directly  from  the  equation : 

W    /         K\ 


PK  D/ 

in  which  L  =  length  of  bearing  in  inches ; 

W  :=  total  load  upon  bearing  in  pounds ; 
P,  K,  N,  and  D  =  same  quantities  as  in  Equation  (5). 

Should  the  length  obtained  by  this  formula  not  give  prac- 
tical dimensions  for  proper  proportions,  the  diameter  and 
length  of  the  bearing  must  be  adjusted  to  meet  the  condi- 
tions. A  good  rule  for  the  length  of  the  journal,  after  the 

Relation  of  Length  1  to  Diameter  d  of  Journals 


Type  of  Bearing 

/ 
Values  of  — 
d 

Marine  engine  main  bearings..    . 

1       to  1  5 

Marine  engine  crankpins 

1       to  1  5 

Stationary  engine  main  journals  

iy2  to  2  5 

Stationary    engine    crankpins  

1 

Stationary   engine   cross-head   pins  

1       to  1  5 

Ordinary  heavy  shafting  with  fixed  bearings     .... 

2       to  3 

Ordinary  shafting  with  self-adjusting  bearings  
Generator    bearings 

3       to  4 
3 

requirements  with  relation  to  the  bearing  pressures  have 
been  met,  is  to  make  the  ratio  of  the  length  to  the  diameter 
about  equal  to  %  of  the  square  root  of  the  number  of  revo- 
lutions per  minute.  This  quantity  may  be  decreased  from 
10  to  20  per  cent  in  the  case  of  crankpins  and  increased 
in  the  same  proportion  in  the  case  of  shaft  bearings,  but 
should  not  be  departed  from  too  widely.  In  the  case  of  an 
engine  making  100  revolutions  per  minute,  the  length  of 
the  bearings  would,  by  this  rule,  be  from  one  and  one- 
quarter  to  one  and  one-half  times  the  diameter.  In  the  case 
of  a  motor  running  at  1000  revolutions  per  minute,  the  bear- 
ings would  be  about  four  diameters  long.  This  rule,  while  it 
cannot  be  adhered  to  on  all  occasions,  is  an  excellent  guide. 


104  DESIGN  OF  PLAIN  BEARINGS 

A  bearing  may  give  poor  satisfaction  because  it  is  too 
long,  as  well  as  because  it  is  too  short.  Almost  every  bear- 
ing is  in  the  condition  of  a  loaded  beam,  and,  therefore,  has 
some  deflection.  Take  the  case  of  an  overhung  crankpin,  in 
order  to  examine  the  phenomena  occurring  in  a  bearing 
under  these  circumstances.  When  the  engine  is  first  run, 
both  the  pin  and  box  are,  or  should  be,  truly  round  and  cyl- 
indrical. As  the  pin  deflects  under  the  action  of  the  load, 
the  pressure  becomes  greater  on  the  side  toward  the  crank 
throw,  breaking  down  the  oil  film  at  that  point,  and  causing 
heat.  After  a  while  the  box,  therefore,  becomes  worn  to  a 
slightly  larger  diameter  at  the  side  toward  the  crank.  The 
box,  as  already  mentioned,  must  be  a  trifle  larger  in  di- 
ameter than  the  journal,  and,  for  successful  working,  this 
difference  is  very  strictly  defined,  and  can  vary  only  within 
narrow  limits.  Should  the  pin  be  too  large,  the  oil  film  will 
be  too  thin,  and  easily  ruptured.  On  the  other  hand,  should 
the  pin  be  too  small  the  bearing  surface  becomes  concen- 
trated at  a  line,  and  the  greater  unit  pressure  at  that  point 
ruptures  the  film.  This  is  also  the  case  when  the  pin  is  too 
long.  The  box  rapidly  wears  large  at  the  inner  end,  and, 
consequently,  the  pressure  becomes  concentrated  along  a 
line.  The  lubricating  film  then  breaks  down,  and  the  pin 
heats  and  scores.  The  remedy  is  not  to  make  the  pin  longer, 
so  as  to  reduce  the  unit  pressure,  but  to  decrease  its  length 
and  to  increase  its  diameter,  causing  the  pressure  to  be 
evenly  distributed  over  the  entire  bearing  surface. 

Examples  of  Calculating  Dimensions  for  Bearings.  A  few 
examples  will  serve  to  make  plain  the  methods  of  designing 
bearings  by  means  of  these  principles. 

Examples :  Design  a  collar  thrust  bearing  for  a  10-inch 
propeller  shaft  running  at  150  revolutions  per  minute,  and 
with  a  thrust  of  60,000  pounds.  Assuming  that  the  thrust 
rings  will  be  2  inches  wide,  their  mean  diameter  will  be  12 
inches.  From  Equation  (5)  the  allowable  bearing  pressure 
is: 

200  x  700 

=  56  pounds  per  square  inch, 

12  X  150  +  700 


DESIGN  OF  PLAIN  BEARINGS  105 

requiring  a  bearing  of  60,000  -*-  56,  or  1070  square  inches 
area.  Since  each  ring  has  an  area  of  0.7854  (142  —  102)  ,  or 
about  75  square  inches,  the  number  of  rings  needed  will  be 
1070  -*•  75,  or  14.  In  case  it  were  desirable  to  keep  down 
the  size  of  this  bearing,  the  constant  K  might  have  been 
given  values  as  high  as  1000  instead  of  700. 

Example:  Design  a  main  bearing  for  a  horizontal 
engine.  Assume  that  the  diameter  of  the  shaft  is  15  inches 
and  that  the  weight  of  the  shaft,  flywheel,  crankpin,  one-half 
of  the  connecting-rod,  and  any  other  moving  parts  that  may 
be  supported  by  the  bearings,  is  120,000  pounds,  and  that 
two-thirds  of  this  weight  comes  on  the  main  bearing,  the 
remainder  coming  on  the  outboard  bearing.  The  engine 
runs  at  100  revolutions  per  minute.  In  this  case,  W  = 
80,000  pounds,  P  =  400  pounds  per  square  inch,  and  K  de- 
pends upon  the  care  and  method  of  lubrication.  Assuming 
that  the  bearing  will  be  flushed  with  oil  by  some  gravity 
system,  and  that,  since  the  engine  is  large,  the  care  will  be 
excellent,  take  K  =  1500.  This  gives  the  length  of  the  bear- 
ing from  Formula  (7)  : 

80,000     /  1500\ 

L  =  00  ^  ~ 


/ 


400  x  1500 

In  computing  the  length  of  this  bearing,  the  pressure  of 
the  steam  is  not  considered  since  it  is  not  a  steady  pressure  ; 
but  the  projected  area  of  the  main  bearing  must  be  greater 
than  the  projected  area  of  the  crankpin. 

Example:  Find  the  dimensions  for  the  bearings  of  a 
100,000-pound  hopper  car  weighing  40,000  pounds,  having 
eight  33-inch  wheels.  The  journals  are  51/2  inches  in  di- 
ameter, and  the  car  is  to  run  at  30  miles  per  hour.  The 
wheels  will  make  307  revolutions  per  minute  when  running 
at  this  speed,  and  the  load  on  each  journal  will  be  140,000 
•*-  8,  or  17,500  pounds.  Although  the  journal  will  be  well 
lubricated  by  means  of  an  oil  pad,  it  will  receive  but  in- 
different care,  so  the  value  of  K  will  be  taken  as  1200.  Using 
these  values,  the  length  of  the  journal  will  then  be  deter- 
mined as  follows  : 


106  DESIGN  OF  PLAIN  BEARINGS 


17,500 


(1200\ 
307  +  luf) 


L  =  800~x          '  3°7  H  )%  inches>aPPro 


Example :  Design  a  crankpin  for  an  engine  with  a 
20-inch  steam  cylinder  running  at  80  revolutions  per  minute, 
and  having  a  maximum  unbalanced  steam  pressure  of  100 
pounds  per  square  inch.  The  maximum  and  not  the  mean 
steam  pressure  should  be  taken  in  the  case  of  crank-  and 
wrist-pins.  The  total  steam  load  on  the  piston  is  31,400 
pounds.  P  will  be  taken  as  1200,  and  K  as  1000.  By 
Formula  (6)  : 

20  X  31,400  x  \/~80 
L  =  =4.7,  or  say,  4%  inches. 

1200  x  1000 

In  order  that  the  deflection  of  the  pin  shall  not  be  suffi- 
cient to  destroy  the  lubricating  film : 


which  limits  the  deflection  to  0.003  inch.  Substituting  in 
this  equation,  the  diameter  becomes  3.85,  or,  say,  3%  inches. 
With  this  diameter,  obtain  the  length  of  the  bearing,  by 
using  Formula  (7)  t 

31,400       /          1000 


( 


L  =1200  x  1000    S(    " 


The  mean  of  this  value  and  the  one  obtained  before  is 
about  7  inches.  Substituting  this  in  the  equation  for  the 
diameter,  D  =  5%  inches.  Substituting  this  new  diameter 
in  Equation  (7)  : 

31,400       /          1000\ 
1  on  -i —  I 


\ 


L=i2ooxi0(481  h"^r;  = 

It  would  now  be  preferable  to  take  about  half  an  inch  off 
the  length  of  this  pin,  and  add  it  to  the  diameter,  making 
it  5%  x  61/2  inches,  and  this  will  be  found  to  bring  the 
ratio  of  the  length  to  the  diameter  nearer  to  one-eighth  of 
the  square  root  of  the  number  of  revolutions. 

Chart  for  Safe  Load  on  Journal  Bearings.  In  overcom- 
ing the  friction  between  a  journal  and  its  bearing,  a  certain 


DESIGN  OF  PLAIN  BEARINGS 


107 


amount  of  energy  is  expended  in  the  form  of  heat,  as  pre- 
viously explained.  The  only  means  of  getting  rid  of  this 
heat  is  by  conduction  from  the  heat  generating  surfaces, 
through  the  masses  of  the  shaft,  bearing  and  bearing  sup- 
port, and  thence  by  radiation  to  the  outside  air.  The  oil 
to  a  certain  extent  serves  as  a  medium  for  the  transfer  of  a 
part  of  the  heat  generated,  by  giving  up  its  heat  to  the  walls 
of  the  oil  chamber ;  but  by  far  the  greater  part  is  dissipated 
by  conduction  in  the  manner  described. 


2500 


012000 


en  1500 
m 

a. 

CO 

z 
plOOO 


500 


\ 


0  100  200  300  400  500  600  700 

LOAD  ON   BEARING  — POUNDS  PER  INCH  OF  LENGTH. Machinery 


Curve  giving   Safe   Load   per  Inch   of  Bearing   Length 

Inasmuch  as  there  is  always  some  heat  generated  in  the 
bearing,  no  matter  how  liberally  it  may  be  designed,  there 
must  always  be  a  temperature  increase  in  the  bearing.  If 
this  heat  can  be  carried  off  as  fast  as  it  is  generated,  the 
bearing  will  at  some  time  in  its  operation  reach  a  constant 
temperature.  As  the  radiating  capacity  of  any  bearing  is 
a  fixed  quantity,  the  temperature  reached  will  depend  on 
the  rate  at  which  heat  is  generated;  therefore,  in  order  that 
a  bearing  may  not  overheat,  there  must  be  some  means  of 
determining  this  rate,  and  fixing  a  limit  to  which  the  amount 
of  heat  generated  may  be  carried.  Between  bearing  sur- 
faces, as  in  all  cases  where  relative  motion  takes  place  be- 


108  DESIGN   OF   PLAIN   BEARINGS 

tween  two  surfaces  in  contact,  the  work  done  in  overcoming 
friction  depends  on  the  rate  of  motion  and  the  pressure 
existing  between  the  two  surfaces.  This  is  modified  to  a  cer- 
tain extent  by  the  character  of  the  surfaces  in  contact,  but 
for  practical  purposes,  it  is  sufficient  to  consider  the  two 
factors  of  speed  and  pressure,  and  as  the  work  done  is  pro- 
portional to  each  it  is  proportional  to  their  product.  By  fix- 
ing the  product  of  these  factors  as  a  constant,  we  have  a 
means  of  limiting  the  work  done  in  the  bearing  to  a  safe 
quantity. 

It  has  been  found  by  observation  of  a  large  number  of 
bearings  that  were  known  to  operate  within  a  temperature 
rise  of  40  degrees  C.  that  if  the  rotative  speed  is  taken  in 
feet  per  minute,  and  the  pressure  in  pounds  per  square  inch 
of  projected  bearing  area,  the  constant  lies  between  the 
limits  of  36,000  and  40,000.  If  we  use  the  smaller  number 
and  let 

d  =  diameter  of  bearing  in  inches, 
I  =  length  of  bearing  in  inches, 

L  =  total  load  on  bearing  in  pounds, 

L 
—  =  P --=  load  on  bearing  per  inch  of  length, 

N  =  revolutions  per  minute, 
we  have, 

*dN       L 

x  —  =  36,000 

12          dl 
which  reduces  to 
NL 

=  137,000,  or  NP  =  137,000 

I 

From  this  we  see  that  if  the  product  of  the  revolutions  per 
minute  and  the  load  on  the  bearing  per  inch  of  length  does 
not  exceed  137,000,  the  bearing  will  operate  within  the  tem- 
perature rise  specified.  By  plotting  these  factors,  the  accom- 
panying curve  was  obtained,  which  presents  this  formula  in 
a  convenient  shape  for  use.  By  reading  across  to  the  curve 


DESIGN  OF  PLAIN  BEARINGS 


109 


from  revolutions  per  minute  at  the  left,  and  thence  down, 
the  safe  load  per  inch  of  bearing  length  will  be  found. 

In  determining  the  pressure  on  the  bearing,  any  load 
due  to  belt  or  chain  pull,  or  gear  thrust,  in  addition  to  the 
direct  weight  of  the  shaft  and  member  carried  by  it,  must 
be  taken  into  account.  In  the  majority  of  cases  the  belt 
pull  will  be  at  an  angle  to  the  direct  weight  on  the  bear- 
ing; the  gear  thrust  may  be  in  any  direction — most  fre- 
quently, however,  in  the  same  direction  or  opposite  to  the 
direct  weight.  In  any  case,  a  resultant  of  the  forces  oper- 
ating on  the  bearing  must  be  taken  and  used  as  the  final 
load  figure. 

Allowance  for  Oil  Between  Shaft  and  Journal  in  Medium 
and  Hig-h-Speed  Bearing-s 


Diameter 
of  Journal 

Allowance 

Diameter 
of  Journal 

Allowance 

Diameter 
of  Journal 

Allowance 

%   to  I 
1%  to  2y2 
2%  to  3y2 

0.002 
0.003 
0.004 

3%  to  4% 
5 
5% 

0.005 
0.006 
0.007 

6 

7 
8 

0.009 
0.011 
0.012 

It  will  be  noted  that  the  diameter  of  the  bearing  does  not 
have  to  be  considered  in  determining  its  safe  load.  While 
it  enters  into  the  formula  as  a  factor  of  the  rotative  speed, 
it  also  has  the  function  of  directly  reducing  the  pressure 
per  square  inch  of  bearing  area,  so  that  it  is  eliminated 
from  the  formula  in  its  final  shape.  The  diameter  of  the 
bearing  is  generally  fixed  from  other  considerations,  being 
chiefly  dependent  upon  the  size  of  shaft  required  for  stiff- 
ness, and  for  transmitting  the  given  horsepower. 

Clearance  between  Journals  and  Bearing  Boxes.  In  de- 
signing journals  and  the  bearing  boxes  in  which  they 
are  to  run,  care  must  be  taken  to  proportion  the  sizes 
of  the  journal  and  its  box  in  such  a  way  that  just  a  suffi- 
cient amount  of  clearance  will  be  left  to  provide  the  nec- 
essary space  for  a  film  of  oil  which  is  required  in  the  bear- 
ing. This  amount  of  clearance  varies  with  the  diameter  of 
the  shaft,  and  in  the  accompanying  table  is  given  the 
clearance  which  should  be  left  for  shafts  of  different  sizes : 


110  DESIGN   OF   PLAIN   BEARINGS 

The  allowances  of  some  manufacturers  are  much  smaller 
than  those  given  in  the  table,  as  indicated  by  the  following 
formula :  The  allowance  made  for  the  "running  fit"  of  the 
box  and  shaft  should  be  about  0.0005  (D  +  1)  inch,  where 
D  is  the  nominal  diameter  of  the  shaft  in  inches. 

Frictional  Losses  in  Babbitt,  Ball,  and  Roller  Bearings.  In 
order  to  determine  the  relative  power  consumption  for 
babbitt,  ball  and  roller  bearings,  a  series  of  tests  was  made 
and  the  results  given  in  a  paper  by  Carl  C.  Thomas,  E.  R. 
Maurer  and  L.  E.  A.  Kelso,  presented  before  the  American 
Society  of  Mechanical  Engineers. 

The  object  of  these  tests  was  to  ascertain  definitely  the 
relative  and  absolute  amounts  of  power  required  to  drive 
a  specially  constructed  lineshaft  carrying  given  loads  at 
certain  known  speeds  of  revolution,  when  supported  suc- 
cessively by  the  three  different  types  of  shaft  bearings 
mentioned,  and  to  determine  coefficients  of  friction  for  each 
type.  Twenty  bearings  of  each  type  were  used  in  order 
that  representative  results  might  be  obtained. 

The  design  of  the  apparatus  was  made  with  the  assist- 
ance of  the  manufacturers  of  the  bearings  to  whom  pre- 
liminary drawings  were  submitted,  and  during  the  four 
years  of  the  tests  representatives  of  these  firms  visited  the 
laboratory  for  the  purpose  of  giving  whatever  advice  and 
assistance  was  possible.  The  preliminary  work,  covering 
the  first  two  years,  showed  the  necessity  of  considering  the 
temperature  of  the  oil  film  in  the  babbitt  and  roller  bear- 
ings, and  it  was  only  after  careful  study  of  the  temperature 
question  with  regard  to  all  three  types  that  satisfactory  re- 
sults were  finally  obtained. 

Description  of  Testing  Apparatus.  The  apparatus  con- 
sists of  25  feet  10  inches  of  lineshafting  in  five  equal  sec- 
tions, mounted  in  hangers  which  are  inverted  and  used  as 
floor  stands.  The  hangers  are  bolted  to  two  8-inch  I-beams 
which  are  leveled  upon  the  floor.  The  shafts  are  of  cold- 
rolled  steel,  2  7/16  inches  in  diameter.  Each  section  is  5 
feet  2  inches  long;  the  adjacent  sections  are  coupled  to- 
gether by  means  of  a  flexible  leather  disk  or  two  straps 


DESIGN  OF  PLAIN  BEARINGS  111 

connecting  the  two  flange  couplings.  The  flexible  couplings 
prevent  transmitting  any  part  of  the  load  applied  on  one 
shaft,  to  either  adjoining  section,  and  also  prevent  binding 
between  shafts  and  bearings  due  to  possible  lack  of 
alignment. 

A  direct-current  Fort  Wayne  motor  is  directly  connected 
to  one  end  of  the  shafting  by  means  of  a  flexible  coupling. 
The  motor  is  of  the  interpole  type  with  the  interpoles  re- 
moved, making  it  a  shunt  motor.  Its  rating  with  the  inter- 
poles  is  71/2  horsepower,  28  amperes,  400/1600  revolution 
per  minute,  four  pole,  230  volts.  The  power  required  to 
run  the  motor  alone  at  all  speeds,  without  load,  was  ac- 
curately ascertained,  as  well  as  the  power  required  to  run 
the  motor  and  shafts  together,  at  all  loads  and  speeds.  The 
relative  amounts  of  power  required  to  overcome  the  friction 
of  the  various  types  of  bearings  were  therefore  accurately 
determined. 

The  load  was  applied  through  levers  having  hardened 
knife  edges  and  pin  points  as  fulcrums.  Across  the  top  of 
the  8-inch  I-beams  and  at  right  angles  to  them,  are  bolted 
short  6-inch  I-beams  to  which  the  fulcrums  are  attached. 
Standard  1000-pound  scales  are  set  upon  the  6-inch  I- 
beams.  A  double  system  of  leverage  is  used  in  order  to  get 
sufficient  load  upon  the  bearings  with  as  short  a  length  of 
lever  as  possible.  This  double  system  of  levers  also  serves 
to  steady  the  apparatus  and  prevent  excessive  vibration. 
A  pressure  ratio  of  8.33  at  each  bearing  to  one  at  the  scale 
was  obtained.  This  was  checked  by  an  independent  method 
of  weighing  the  actual  load  resulting  at  the  bearings,  from 
a  given  load  on  the  scales.  The  loads  were  applied  to  the 
shaft  by  two  bearings  between  each  pair  of  hangers.  These 
bearings  are  identical  with  those  in  the  hangers,  and  are 
supplied  with  knife  edges  which  engage  a  V-shaped  groove 
in  the  5-inch  I-beam  levers.  The  bearings  and  hangers  for 
each  section  are  symmetrically  placed  with  respect  to  the 
middle  of  the  section;  therefore,  equal  loads  on  the  inter- 
mediate bearings  produce  equal  pressures  on  the  end  bear- 
ings. The  reason  for  using  twenty  bearings  was  that  the 
amount  of  power  necessary  for  a  single  bearing  was  so 


112  DESIGN  OF  PLAIN  BEARINGS 

small  as  to  be  difficult  of  measurement ;  moreover  any  single 
bearing  might  not  truly  represent  results  that  would  be  ob- 
tained from  that  type  of  bearing  in  general. 

The  Bearings  Tested.  The  three  kinds  of  bearings 
tested  were :  the  Hess-Bright  ball  bearing  manufactured  by 
the  Hess-Bright  Mfg.  Co.;  the  ring-oiled  bearing  manu- 
factured by  the  Dodge  Mfg.  Co.,  lined  with  babbitt  metal 
made  from  their  formula;  and  the  Hyatt  roller  bearing 
manufactured  by  the  Hyatt  Roller  Bearing  Co.  All  bear- 
ings were  for  the  same  size  shaft  and  the  same  pieces  of 
shafting  were  used  for  all  the  tests,  except  that  two  sec- 
tions bent  during  the  tests  were  replaced.  The  babbitt 
bearings  are  9  21/32  inches  long  and  hence  their  projected 
area  is  22.36  square  inches.  These  bearings  were  oiled 
by  the  well-known  ring-oiler  device,  there  being  two  rings 
in  each  bearing.  Each  roller  bearing  contains  six  right- 
hand  and  six  left-hand  rollers,  0.780  inch  in  diameter;  six 
are  9  9/16  inches  long  and  six  are  9  3/16  inches  long.  The 
bearings  are  of  the  type  in  which  a  cage  is  used  for  hold- 
ing one-half  the  rollers.  Each  ball  bearing  contains  a  single 
set  of  balls  9/16  inch  in  diameter.  The  diameter  of  the 
inner  race  across  the  ball  groove  is  3.4729  inches. 

Mercury  thermometers  (two  in  each  babbitt  and  roller 
bearing,  and  one  in  each  ball  bearing)  were  used  for  meas- 
uring the  temperature  of  the  oil  or  bearing.  In  order  to 
avoid  the  endwise  thrust  of  the  shaft,  when  supported  by 
the  roller  bearings,  it  was  necessary  to  interpose  two  ball 
thrust  collars.  Before  this  was  done,  excessive  vibration 
of  the  motor  and  of  the  apparatus  resulted  from  the  ten- 
dency of  the  shaft  to  move  endwise.  This  was  particularly 
troublesome  at  high  loads  and  speeds. 

Procedure  when  Making  Tests.  The  power  was  meas- 
ured by  the  ammeter  voltmeter  method.  A  second  ammeter 
was  used  as  a  check  on  the  first;  and  a  watt-meter  (ar- 
ranged for  direct  and  reverse  readings)  as  a  further  check. 
The  general  order  of  taking  data  was  as  follows:  Clean 
the  commutator;  adjust  motor  to  speed;  take  all  power 
readings;  read  all  thermometers;  adjust  speed  again  and 


DESIGN   OF   PLAIN   BEARINGS 


113 


repeat  power  measurements.  This  gave  the  power  both 
before  and  after  the  temperature  was  taken,  the  mean  of 
which  would  give  the  mean  power  for  the  mean  tempera- 
ture  very  closely.  In  addition,  the  readings  acted  as  a 
check  on  each  other. 

The  manner  of  making  a  test  or  run  was  essentially  as 
follows:  Each  night  the  plant  was  run  from  three  to 
twelve  hours  under  the  load  and  speed  to  be  used  during 
the  run  of  the  following  day,  but  without  observation.  The 
purpose  of  the  preliminary  night  run  was  to  allow  the  shaft 
and  bearings  to  adjust  themselves  to  the  conditions  of  the 
run.  Then  on  the  following  day  the  shaft  was  run  from 
three  to  six  hours  and  frequent  observations  of  power  and 

Relative  Amounts  of  Power  Consumed  in  Friction 


Bearings 

100  Feet  per  Minute 

300  Feet  per  Minute 

77  Deg.  F. 

100  Deg.  F 

77  Deg.  F. 

100  Deg.  F 

Ball    

1 

2.2 
3 

1 
2.5 
3.6 

1 
2.7 
4.5 

1 
3 
4 

Roller  

Babbitt     

temperature  were  made  during  the  run.  The  first  few 
observations  were  made  as  often  as  practicable  (about  five 
minutes  apart)  ;  the  others,  generally  at  fifteen-minute  in- 
tervals, but  toward  the  end  of  the  run  when  the  tempera- 
ture was  rising  slowly  observations  were  made  at  longer 
intervals  which  were  generally  of  thirty  minutes  or  more 
in  duration. 

The  speeds  used  in  the  tests  were  between  150  and  450 
revolutions  per  minute,  corresponding,  respectively,  to  about 
100  and  300  feet  per  minute  peripheral  speed.  Most  of  the 
loads  used  were  between  700  and  1800  pounds  per  bearing, 
corresponding,  respectively,  to  about  30  and  80  pounds  per 
square  inch  for  the  babbitt  bearings  All  statements  of  re- 
sults therefore  are  subject  to  the  above  limitations  as  to 
speed  and  loads.  Two  lubricants  were  used  in  all  the  tests : 
Atlantic  red  engine  oil  in  the  babbitt  and  roller  bearings, 
and  No.  2  Keystone  grease  in  the  ball  bearings. 


114 


DESIGN  OF  PLAIN  BEARINGS 


Relative  Power  Consumption.  A  comparison  was  made 
of  the  power  consumed  by  friction  in  the  babbitt,  roller  and 
ball  bearings  for  bearing  temperatures  of  100  degrees  and 
77  degrees  F.,  respectively.  The  power  required  for  the 
babbitt  bearings  is  higher  than  for  the  other  bearings,  ex- 
cept perhaps  at  low  loads  and  speed,  and  the  power  for 
roller  bearings  is  higher  than  for  ball  bearings.  The  ex- 
cess of  power  for  babbitt  over  rollers,  and  rollers  over  balls, 
increases  with  increase  of  speed  for  all  loads.  The  table, 
"Relative  Amounts  of  Power  Consumed  in  Friction,"  shows 
the  power  consumed  in  friction  by  the  three  kinds  of  bear- 
ings at  the  speeds  and  temperatures  indicated ;  the  relative 
numbers  are  based,  in  each  case,  on  the  average  power  for 

Comparison  of  Coefficients  of  Friction 


Type 
of 
Bearing 

Coefficient    of    Friction 

Load,  727  Pounds 

Load,  1227  Pounds 

Load,  1727  Pounds 

77  Deg. 

0.0025 
0.0069 
0.0112 

100  Deg. 

77  Deg. 

100  Deg. 

77  Deg. 

100  Deg. 

Ball 

0.0019 
0.0055 
0.0075 

0.0022 
0.0055 
0.0082 

0.0018 
0.0047 
0.0058 

0.0020 
0.0049 
0.0070 

0.0016 
0.0042 
0.0051 

Roller  
Babbitt    

the  three  loads :  710,  1210,  and  1710  pounds  for  balls ;  740, 
1240,  and  1740  for  rollers;  and  730,  1230,  and  1730  for 
babbitt. 

The  coefficients  of  friction  for  the  three  types  of  bear- 
ings, when  subjected  to  average  loads  of  727,  1227  and 
1727  pounds,  respectively,  and  temperatures  of  77  and  100 
degrees  F.,  are  given  in  table,  "Comparison  of  Coefficients 
of  Friction."  The  peripheral  speed  was  150  feet  per 
minute. 

Lubricant  Breakdown  Tests.  In  order  to  observe  the  per- 
formance of  the  bearings  under  extraordinarily  heavy 
loads,  "breakdown  tests"  were  run  on  each  type  of  bearing 
with  only  one  section  of  shafting  on  which  were  four  bear- 
ings. This  small  number  of  bearings  was  used  because  it 
was  impracticable  to  keep  close  watch  of  a  larger  number 
and  avoid  trouble  during  the  excessively  severe  conditions. 


DESIGN  OF  PLAIN  BEARINGS  115 

The  maximum  load  was  600  pounds  on  the  scales,  or  about 
5000  pounds  per  bearing.  A  speed  of  200  revolutions  per 
minute  was  chosen  because  it  represents  about  the  average 
lineshaft  speed  in  practice.  These  tests  began  at  about 
3200  pounds  per  bearing.  Failure  occurred  at  about  4250 
pounds  per  bearing  in  the  case  of  the  babbitt,  4650  pounds 
in  the  case  of  the  ball  bearings,  and  about  5100  pounds  in 
the  case  of  the  roller  bearings. 

The  quality  and  amount  of  lubricant  used  undoubtedly 
have  an  important  effect  upon  the  load  that  will  cause  a 
given  bearing  to  fail.  The  bearings  did  not  in  any  case 
fail  structurally,  as  the  power  was  cut  off  soon  after  dis- 
tress was  manifested,  but  the  failure  was  simply  that  of  the 
lubricant.  Breaking  down  of  the  lubricant  resulted  in  an 
immediate  increase  of  the  power  required  to  maintain 
the  original  speed  of  rotation  of  the  shaft  in  the  bearings. 
In  each  case  probably  only  one  of  the  four  bearings  used 
in  the  breakdown  tests  showed  distress  at  any  one  time. 
In  the  case  of  ball  bearings,  distress  was  manifested  by  dis- 
integration of  the  grease  which  "melted"  and  ran  out  of  the 
bearing.  This  was  accompanied  by  the  immediate  increase 
in  power  requirement.  Similar  behavior  on  the  part  of  the 
babbitt  and  the  roller  bearings  indicated  that  at  least  one 
of  the  four  under  test  was  suffering  from  an  approach  to 
"metal-to-metal"  contact.  The  bearings  were  not  injured 
by  these  endurance  tests,  and  all  were  used  in  subsequent 
tests  at  the  more  usual  speeds  and  pressures. 


INDEX 


Adjustable  bearings,  1 

for  machine  tool  spindles,  3 
Alloys  for  bearing  metals,  40 
Alloys  for  bearings,  comparison 

between  hard  and  soft,  30 
containing  antimony,  32 
copper,  tin  and  lead,  39 
lead  and  antimony,  33 
lead,  antimony  and  tin,  34 
metals  used  in,  32 
tin  and  antimony,  34 
tin,  antimony  and  copper,  34 
tin,  antimony,  lead  and  copper, 

34 

American  Society  for  Testing  Ma- 
terials' specifications  for  bab- 
bitt metals,  36 
Antimony,  alloys  containing,  32 

alloys  of  lead  and,  33 
Antimony,    lead    and    tin,    alloys 

of,  34 
Antimony,  tin  and  copper,  alloys 

of,  34 
Antimony,   tin,   lead   and   copper, 

alloys  of,  34 

Automatic  lubrication,  bronze 
bushing  with  provision  for, 
80 

Babbitt,  ball  and  roller  bearings, 

frictional  losses  in,  110 
effect  of  lead  on,  45 
for  sub-press  slides,  36 
Babbitted    and    cast-iron    spindle 

bearings,  15 
Babbitt  metal,  35 
American    Society    for    Testing 
Materials'    specifications    for, 
36 
Brinell  hardness  tests  on,  43 


composition  of,  35 

effect    of    compression    on    Bri- 
nell hardness  of,  45 

lead-base  and  tin-base,  compari- 
son of,  43 

properties  of,  37 

S.  A.  E.  standard,  37 
Ball,  babbitt  and  roller  bearings, 

frictional  losses  in,   110 
Bearing      box,       adjustable,       of 
straight  cylindrical  form,  9 

clearance  between  journal  and, 
109 

compensation  for  wear  by  com- 
pressing, 14 
Bearing    dimensions,    calculating, 

100,  104 
Bearing  metals,  29 

bronze,  38 

commercial,  40 

composition  of  alloys  used  for, 
40 

miscellaneous,  47 

principal  requirements  of,  30 

substitutes  for  tin  in,  42 

tests  on,  48 
Bearing     pressures     for     various 

classes  of  bearings,  99 
Bearings,    allowance    for    oil    be- 
tween   shaft    and    journal    in 
medium  and  high-speed,  109 

compensation  for  wear  of,  14,  15 

generation  of  heat  in,  97 

grinding  wheel   spindle,   4 

hard  and   soft  alloys  for,  com- 
parison between,  30 

high-speed,  102 

lubricated      and      unlubricated, 
frictional  resistance  in,  95 


117 


118 


INDEX 


methods  of  lubricating,  50 
oiled  by  splash  system,  82 
oil  grooves  for,  90 
plain,  design  of,  93 
plain,  types  of,  1 
provision  for  cleaning,  11 
ring-oiled  disk  grinder,  59 
ring-oiling,  rings  for,  62 
types  of  self-oiling,  78 

Brinell  hardness  tests  on  babbitt 
metals,  43 

Bronze,  29 

composition  of,  42 
containing  copper,  tin  and  lead, 
39 

Bronze  bearing  metals,  38 

Capillary  lubrication,  multiple,  77 
Capillary       self-oiling       bearings, 

Dodge,  78 
Cast-iron     and     babbitt     spindle 

bearings,  15 
Cleaning  bearings,  provision   for, 

11 
Coefficients  of  friction  for  babbitt, 

ball  and  roller  bearings,   113 
Collar  thrust  bearings,  26 
Copper,  antimony  and  tin,  alloys 

of,  34 
Copper,   antimony,   lead    and    tin, 

alloys  of,  34 

Copper,  tin  and  lead,  bronze  con- 
taining. 39 

Design,  milling  machine   spindle 

bearing,  9 
of   bearings,   general   principles 

governing,  94 
of  plain  bearings,  93 
thrust  bearing,   based   on   prin- 
ciple    of     wedge-shaped     oil 
film,  27 

Dimensions  of  bearings,  calculat- 
ing, 100,  104 

Dodge    capillary    self-oiling    bear- 
ings, 78 


Felt  pads,  lubrication  by,  55 

Flat  surfaces,  lubrication  of,  70 

Flooded  lubrication,  84 

Frictional  losses  in  babbitt,  ball 
and  roller  bearings,  110 

Frictional  resistance  in  lubricated 
and  unlubricated  bearings,  95 

Friction,  comparison  of  coeffici- 
ents of,  for  babbitt,  ball  and 
roller  bearings,  113 

Grease  lubrication,  77 

Grinding  wheel  spindles,  bearings 

for,  4 
Grinding    wheel    spindle    bearing, 

vertical,  lubricating,  74 

Heat,  generation  of   in  bearings, 

97 
High-speed  bearings,  102 

Journal  bearings,  1 

chart  for  safe  load  on,  106 

Journals,  relation  of  length  to  di- 
ameter, 103 

Journals  and  bearing  boxes,  clear- 
ances between,  109 

Lead  and  antimony,  alloys  of,  33 
Lead,  antimony  and  tin,  alloys  of, 

34 
Lead,   antimony,   tin   and   copper, 

alloys  of,  34 

Lead,  effect  of,  on  babbitt,  45 
Lead,  tin  and  copper,  bronze  con- 
taining,  39 
Lineshaft  hanger  bearings,  oiling, 

88 
Load    on    journal   bearings,    safe, 

chart  for,  106 

Load  on  thrust  bearings,  25 
Lubricant  breakdown  tests,  114 
Lubricating  bearings,  methods  of, 

50 
Lubricating  devices,  examples  of, 

54 

Lubrication,      automatic,      bronze 
bushing  with  provision  for,  80 


INDEX 


119 


by  felt  pads,  55 
flooded,  84 

grease,   provision   for,  77 

multiple  capillary,  77 

of  flat  sliding  surfaces,  70 

of      vertical      grinding      wheel 
spindle  bearing,  74 

of  vertical  spindles,  73 

splash  system  of,  82 

submerged,     for     bearing     sur- 
faces, 80 

Lubricants,  methods  of  supplying, 
to  bearings,  53 

piping  for  conducting,  66 

Machine   tools,    adjustable    bear- 
ings for  spindles  of,  3 
Metals,  babbitt,  35 

babbitt,   lead-base   and   tin-base 

compared,  43 
bearing,  29 

bearing,    commercial,   40 
bearing,  miscellaneous,  47 
bearing,  tests  on,  48 
used  in  bearing  alloys,  32 
white,  29 

Milling   machine   spindle   bearing 
design,  9 

Oil,  allowance  for,  between  shaft 
and   journal   in   medium   and 
high-speed  bearings,  109 
conducted  by  wicks,  64 
distribution,  52 
influence  of  quality  of,  98 
quantity  of,  51 
Oil  baths  for  submerging  bearing 

surfaces,  80 
Oil  ducts,  special,  65 
Oil     film,     wedge-shaped,     thrust 
bearing  design  based  on  prin- 
ciple of,  27 

Oil  grooves  for  bearings,  90 
Oiling  lineshaft  hanger  bearings, 

88 

Oiling,  ring,  58 
Oiling  rings  or  disks,  fixed,  63 


Oilless  bearings,  18 
Oil  supply  for  bearings,  how  ef- 
fected, 50 
Oil  tanks,  elevated,  87 

Piping  for  conducting  lubricants, 
66 

Plain  bearings,  design  of,  93 
types  of,  1 

Power    consumption,    relative,    of 
babbitt,    ball    and    roller    bear- 
ings, 113,  114 

Pressure,  allowable,  in  pounds  per 
square  inch,  on  thrust  bear- 
ings, 26 

Radial  bearings,  1 

Ring  oiling,  58 

applied  to  diok  grinder  bear- 
ings, 59 

Ring-oiling  bearings,  rings  for,  62 

Roller,  babbitt  and  ball  bearings, 
frictional  losses  in,  110 

S.  A.  E.  standard  babbitt  metal,  37 
Schiele  curve,  the,  22 
Self-adjusting  vertical  bearings,  8 
Self-aligning  bearings,  1 
Self-aligning  spindle  bearings,  5 
Self-oiling  bearings,  types  of,  78 
Shaft  or  pin,  diameter  of,  in  high- 
speed bearings,  102 
Solid  bearings,  1 
Spindle  bearings,  self-aligning,  5 
Splash  system  of  lubricating  bear- 
ings, 82 
Step    bearings,    simple,    for   light 

duty,  22 
Sub-press  slides,  babbitt  for,  36 

Tables,  allowance  for  oil  between 
shaft  and  journal  in  medium 
and  high-speed  bearings,  109 

alloys  used  for  bearing  metals, 
composition  of,  41 

babbitt  metal  compositions,  35, 
36 


120 


INDEX 


bearing  metals,  miscellaneous, 
48 

bearing  pressures  for  various 
classes  of  bearings,  99 

bronzes,  composition  of,  42 

coefficients  of  friction,  compari- 
son of,  for  babbitt,  ball  and 
roller  bearings,  114 

friction,  relative  amounts  of 
power  consumed  in,  by  bab- 
bitt, ball  and  roller  bearings, 
113 

journals,  relation  of  length  to 
diameter,  103 

thrust  bearings,  allowable  pres- 
sure in  pounds  per  square 
inch,  26 

Tanks,  oil,  elevated,  87 
Testing    power     consumption     of 
babbitt,  ball  and  roller  bear- 
ings, 110 

Tests,  lubricant  breakdown,  114 
Thrust  bearings,  1,  21,  25 

allowable  pressure  in  pounds 
per  square  inch,  26 


design    based    on    principle    of 

wedged-shaped  oil  film,  27 
load  on,  25 
Tin,  antimony  and  copper,  alloys 

of,  34 
Tin,    antimony    and    lead,    alloys 

of,  34 
Tin,   antimony,   lead   and   copper. 

alloys  of,  34 
Tin,  lead  and  copper,  bronze  con 

taining.  39 
Tin,    substitutes    for,    in    bearing 

metals,  42 

Vertical  bearings,   self-adjusting, 

8 
Vertical   spindles,   lubrication   of, 

73 

Wear  in   bearing,   compensation 
for,    by     compressing    bearing 

box,  14 

compensation    for,    by    drawing 
spindle  into  tapered   box,   15 
White   Metal,   29 
Wicks,  oil  conducted  by,  64 


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